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Basic and clinical Biostatistics 4th ronaldweinland.info - Ebook download as PDF File .pdf ), for the enthusiastic support of the current and former staff of Lange Medical. (c) - page 1 of 7 - Get Instant Access to PDF File: 6bd3 Basic & Clinical Biostatistics: Fourth Edition (Lange Basic Science) By. Basic & Clinical Biostatistics, 4e. Beth Dawson, Robert G. Trapp. Go to Review Questions. Search Textbook Autosuggest Results. Chapter 1. Introduction to.
Please insert serial number when requested by the program. System Requirements 32 bit version of Windows Windows 98 or later. Pentium processor running at 66mHz. This goal has guided us in the selection of material and in the presentation of information. This chapter outlines the reasons physicians, medical students, and others in the health care field should know biostatistics. It also describes how the book is organized, what you can expect to find in each chapter, and how you can use it most profitably. It derives from the Latin word status, meaning manner of standing or position.
Information in Chapters 4 and 12 relates particularly to skills for interpreting diagnostic tests. Being Informed Keeping abreast of current trends and being critical about data are more general skills and ones that are difficult to measure.
These skills are also not easy for anyone to acquire because many responsibilities compete for a professional's time. One of the byproducts of working through this text is a heightened awareness of the many threats to the validity of information, that is, the importance of being alert for statements that do not seem quite right.
Appraising Guidelines The number of guidelines for diagnosis and treatment has increased greatly in recent years. Practitioners caution that guidelines should not be accepted uncritically; although some are based on medical evidence, many represent the collective opinion of experts. Health practitioners, of course, have the expertise to evaluate the content of a protocol or article, but they often feel uncomfortable about critiquing the design and statistical methods of a study.
No study, however important, will provide valid information about the practice of medicine and future research unless it is properly designed and analyzed.
Careful attention to the concepts covered in this text will provide physicians with many of the skills necessary for evaluating the design of studies. Participating in or Directing Research Projects Clinicians participating in research will find knowledge about biostatistics and research methods indispensable.
Residents in all specialties as well as other health care trainees are expected to show evidence of scholarly activity, and this often takes the form of a research project.
The comprehensive coverage of topics in this text should provide most of them with the information they need to be active participants in all aspects of research. We have designed a comprehensive text covering the traditional topics in biostatistics plus the quantitative methods of epidemiology used in research.
For example, we include commonly used ways to analyze survival data in Chapter 9; illustrations of computer analyses in chapters in which they are appropriate, because researchers today use computers to calculate statistics; and applications of the results of studies to the diagnosis of specific diseases and the care of individual patients, sometimes referred to as medical decision making or evidence-based medicine.
We have added a number of new topics to this edition and have extended our coverage of some others. We have enhanced our discussion of evidence-based medicine and continue to emphasize the important concept of the number of patients that need to be treated with a given intervention in order to prevent one undesirable outcome number needed to treat.
The likelihood ratio, often presented in many journal articles that evaluate diagnostic procedures or analyze risk factors, is covered in more detail.
We continue to use computer software to illustrate the discussion of the number of subjects needed in different types of studies power. We have increased our coverage of the increasingly important multivariate methods, especially logistic regression and the Cox proportional hazard model.
The chapters on survival methods and analysis of variance have been revised. Due to several suggestions, P. Our approach deemphasizes calculations and uses computer programs to illustrate the results of statistical tests. In most chapters, we include the calculations of some statistical procedures, primarily because we wish to illustrate the logic behind the tests, not because we believe you need to be able to perform the calculations yourself. Some exercises involve calculations because we have found that some students wish to work through a few problems in detail so as to understand the procedures better.
The major focus of the text, however, is on the interpretation and use of research methods. A word regarding the accuracy of the calculations is in order. Many examples and exercises require several steps. The accuracy of the final answer depends on the number of significant decimal places to which figures are extended at each step of the calculation; we generally extend them to two or three places. Calculators and computers, however, use a greater number of significant decimal places at each step and often yield an answer different from that obtained using only two or three significant digits.
The difference usually will be small, but do not be concerned if your calculations vary slightly from ours. The examples used are taken from studies published in the medical literature.
Occasionally, we use a subset of the data to illustrate a more complex procedure. In addition, we sometimes focus on only one aspect of the data analyzed in a published study in order to illustrate a concept or statistical test.
To explain certain concepts, we often reproduce tables and graphs as they appear in a published study. These reproductions may contain symbols that are not discussed until a later chapter in this book.
Simply ignore such symbols for the time being. We chose to work with published studies for two reasons: First, they convince readers of the relevance of statistical methods in medical research; and second, they provide an opportunity to learn about some interesting studies along with the statistics. We have also made an effort to provide insights into the coherency of statistical methods.
We often refer to both previous and upcoming chapters to help tie concepts together and point out connections. This technique requires us to use definitions somewhat differently from many other statistical texts; that is, terms are often used within the context of a discussion without a precise definition. The definition is given later.
Several examples appear in the foregoing discussions eg, vital statistics, means, standard deviations, proportions, rates, validity.
We believe that using terms properly within several contexts helps the reader learn complex ideas, and many ideas in statistics become clearer when viewed from different perspectives. Some terms are defined as we go along, but providing definitions for every term would inhibit our ability to point out the connections between ideas.
To assist the reader, we use boldface for terms the first few times they are used that appear in the Glossary of statistical and epidemiologic terms provided at the end of the book. For example, many of the same principles are involved in methods to summarize and display data, so these are now in the same chapter Chapter 3 and discussed in an integrated manner.
Most biostatistical texts, our previous editions included, divide the methods into chapters, with, for example, a chapter on t tests, another chapter on chi-square 2 tests, and so forth. In this edition, we organize the methods to relate to the kind of research question being asked.
Therefore, there is a chapter on analyzing research questions involving one group of subjects Chapter 5 , another chapter on research questions involving two groups of subjects Chapter 6 , and yet another on research questions involving more than two groups of subjects Chapter 7.
We believe this organization is more logical, and we hope it facilitates the learning process. Each chapter begins with two components: key concepts and an introduction to the examples presenting problems covered in the chapter.
The key concepts are intended to help readers organize and visualize the ideas to be discussed and then to identify the point at which each is discussed.
At the conclusion of each chapter is a summary that integrates the statistical concepts with the presenting problems used to illustrate them. The flowcharts are grouped in Appendix C for easy reference.
Patients come to their health care providers with various health problems. In describing their patients, these providers commonly say, The patient presents with or The patient's presenting problem is We use this terminology in this text to emphasize the similarity between medical practice and the research problems discussed in the medical literature.
Almost all chapters begin with presenting problems that discuss studies taken directly from the medical literature; these research problems are used to illustrate the concepts and methods presented in the chapter.
In chapters in which statistics are calculated eg, the mean in Chapter 3 or statistical procedures are explained eg, the t test in Chapters 5 and 6 , data from the presenting problems are used in the calculations. We try to ensure that P. As advances are made in medicine, however, it is possible that some of this content will become outdated; we will attempt to correct that in the next edition. We have attempted to select presenting problems that represent a broad array of interests, while being sure that the studies use the methods we want to discuss.
Beginning with the third edition, we incorporated data from a number of investigators, who generously agreed to share their data with us, and we have continued that practice in the fourth edition.
Furthermore, many authors agreed to let us publish a subset of their data with this text, thus providing us with a number of advantages: We can use real data in the statistical programs, and readers can use the same data to reinforce and extend their knowledge of the methods we discuss. Sometimes we focus on only a small part of the information presented in the article itself, but we usually comment on their findings in the summary of the chapter.
We have tried not to misinterpret any of the data or reported findings, and we take responsibility for any errors we may have committed in describing their research. We recommend that our readers obtain a copy of the original published article and use it, along with our discussion of the study, to enhance their clinical knowledge as well as their statistical expertise.
This edition continues the inclusion of actual data and software on the CD-ROM that accompanies this text. The data sets are provided in several different formats to make it easy to use them for statistical analysis.
The software is that developed by Dr. We have used this software for a number of years and find it comprehensive and easy to use. Many of the illustrations of the statistical procedures in this book were facilitated by using NCSS, and we hope our readers use it to replicate the analyses and to do the exercises. As an added benefit, the procedures included on this version of NCSS can also be used to analyze other data sets.
We have established an Internet Web site to provide you with the most up-to-date information and additional resources on biostatistics.
We appreciate the communications from readers of the previous editions; it helps us try to make the next edition better.
Some statistical tests are not routinely available on most commercial packages. We have designed a spreadsheet program to analyze these special instances. These files are included in a folder on the CD named Calculations. Exercises are provided with all chapters ; answers are given in Appendix B, most with complete solutions.
We include different kinds of exercises to meet the different needs of students. Some exercises call for calculating a statistic or a statistical test. Some focus on the presenting problems or other published studies and ask about the design as in Chapter 2 or about the use of elements such as charts, graphs, tables, and statistical methods.
Occasionally, exercises extend a concept discussed in the chapter. This additional development is not critical for all readers to understand, but it provides further insights for those who are interested. Some exercises refer to topics discussed in previous chapters to provide reminders and reinforcements. Again, we highly recommend that you obtain copies of the original articles and review them in their entirety.
If you are using this book in an organized course, we suggest you form small groups to discuss the articles and examine how the concepts covered in the book are dealt with by the various researchers. Finally, in response to a plea from our own students, a collection of multiple-choice questions is given in Chapter 13 ; these questions provide a useful posttest for students who want to be sure they have mastered the material presented in the text.
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A comprehensive user-friendly introduction to biostatistics and epidemiology applied to medicine, clinical practice, and research. Features "Presenting Problems" case studies drawn from studies published in the medical literature, end-of-chapter, and a CD-ROM with data sets and statistical software programs. Show all links. Allow this favorite library to be seen by others Keep this favorite library private.
Find a copy in the library Finding libraries that hold this item Studies with interventions are called experiments or clinical trials.
If you are familiar with the medical literature. Bias occurs when the way a study is designed or carried out causes an error in the results and conclusions. The authors wanted to compare two methods to see which better predicted peak systolic velocity. Cohort and case —control studies generally involve an extended period of time defined by the point when the study begins and the point when it ends.
Causes and incidence of disease 2. Kleinbaum and colleagues describe a number of hybrids or combinations of these designs if you are interested in more detail than we give in this chapter. Not randomized 2. Meta-analyses Case—series studies frequently lead to the generation of hypotheses that are subsequently investigated in a case —control.
Sequential controls a. Cohort studies prospective 1. Classification of study designs. They concluded that the relationship between both methods and peak systolic velocity was very strong. Randomized b. Studies with no controls III. Disease description 2. Diagnosis and staging 3. Each study design in Table is illustrated in this chapter. Descriptive or case—series B. If you would like a more detailed discussion of study designs used in medicine. Table Observational studies A. Parallel or concurrent controls a.
Crossover 3. For this reason. Natural history. Experimental studies involve an intervention—an investigator-controlled maneuver.
Some investigators would not include case— series in a list of types of studies because they are generally not planned studies and do not involve any research hypotheses. Case—series reports generally involve patients seen over a relatively short time. Case—control studies retrospective 1.
Experimental studies A. Generally case—series studies do not include control subjects. Self-controlled b. When certain characteristics of a group or series of patients or cases are described in a published report.
In observational studies. Identification of risk factors E. The cross-sectional study analyzes data collected on a group of subjects at one time. The major difference between them is the direction of the inquiry or the focus of the research question: Cohort studies are forward-looking. Controlled trials 1. Case—Control Studies Case—control studies begin with the absence or presence of an outcome and then look backward in time to try to detect possible file: Case—Series Studies A case—series report is a simple descriptive account of interesting characteristics observed in a group of patients.
Garb and Burns and Grove discuss study design in medicine and nursing. Identification of risk factors C. External controls including historical B. Disease processes. A book by Hulley and Cummings is devoted entirely to the design of clinical research. Cross-sectional studies. Historical cohort studies II. These three types of studies are defined by the period of time the study covers and by the direction or focus of the research question. On occasion. Alexandrov and coworkers presented information on a series of 40 patients who had been referred for evaluation of stroke.
We mention case—series studies because of their important descriptive role as a precursor to other studies. Investigators sometimes use matching to associate controls with cases on characteristics such as age and sex.
If an investigator feels that such characteristics are so important that an imbalance between the two groups of patients would affect any conclusions.
If the purpose is simple description. Vol 8. The histories of cases and controls are examined over a previous period to detect the presence shaded areas or absence unshaded areas of predisposing characteristics or risk factors. Subjects are selected and information is obtained in a short period of time Figure Retrospective studies.
Surveys and polls are generally cross -sectional studies. Cross-sectional studies analyze data collected on a group of subjects at one time rather than over a period of time. In case— control designs. The cases in case—control studies are individuals selected on the basis of some disease or outcome. Deciding whether a published study is a case—control study or a case—series report is not always easy.
The easiest way to differentiate between them is to ask whether the author's purpose was to describe a phenomenon or to attempt to explain it by evaluating previous events. Cross-Sectional Studies The third type of observational study goes by all of the following names: Case—control studies are longitudinal as well. Adapted and reproduced. Olsen and colleagues compared patients who had a surgical site infection following laminectomy or spinal fusion cases with patients who developed no infection controls.
Cross-sectional studies may be designed to address research questions raised by a case—series. Schematic diagram of case—control study design. Figure illustrates that subjects in the study are chosen at the onset of the study after they are known to be either cases with the disease or outcome squares or controls without the disease or outcome diamonds.
The investigators found that length of hospital stay and readmission rates were greater with patients with infections. Johnson NL [editors]: Encyclopedia of Statistical Sciences. The history or previous events of both cases and controls are analyzed in an attempt to identify a characteristic or risk factor present in the cases' histories but not in the controls' histories. Squares represent subjects with the outcome of interest. Because they focus on a point in time.
In Kotz S. Shaded areas represent subjects exposed to the antecedent factor. This process ensures that both groups will be similar with respect to important characteristics that may otherwise cloud or confound the conclusions. Figure Confusion arises because both types of studies are generally conceived and written after the fact rather than having been planned.
Many times investigators use preexisting surveys rather than creating their own. These patients could be targeted for assessment of alcohol abuse and dependence and other possible substance abuse. Schematic diagram of cross -sectional study design. Surveys are generally cross -sectional in design. It is important to establish the level of agreement between the MRI findings and histology. They wanted to develop a simple scoring system that could be used to detect these patients when they come to an emergency department.
This was true for two measures of the autoimmune nervous system function. These two measures. Often these limits are established by testing people who are known to have normal values. After comparing certain demographic groups. Establishing Norms Knowledge of the range within which most patients fit is very useful to clinicians.
Caiola and Litaker wanted to know the factors that influence fellows to select a specific general internal residency fellowship program. We examine this study in more detail in Chapter 11 P. Soderstrom and his coinvestigators were interested in learning more about the relationship between demographic measures that might be helpful in identifying trauma patients who have an elevated blood alcohol concentration.
These values are called normal values. Using these four simple measures. Patenaude and colleagues asked medical students at a Canadian medical school to complete a questionnaire on moral file: Because they did not know the names and addresses of the fellows. Surveys Surveys are especially useful when the goal is to gain insight into a perplexing topic or to learn how people think and feel about an issue.
The histology slides were evaluated by a pathologist who was blinded to the imaging results. They chose to look at the time of day day or night.
Evaluating Different Methods of Doing the Same Thing A presenting problem in Chapter 5 is a cross-sectional study designed to examine the relationship between histology slides and magnetic resonance imaging MRI to study characteristics of diseased carotid arteries Yuan et al.
Cross-sectional studies are used in all fields of medicine. We would not. Outside of the laboratory there are many qualities for which normal ranges have not been established.
Gelber and colleagues analyzed data from subjects recruited from 63 centers throughout North America to develop normative values for these two measurements.
Although the Framingham Heart Study is very long term. All subjects are followed over a certain period to observe the effect of the risk factor or exposure. Many studies deal with cardiovascularrelated conditions for which the study was designed. Because the events of interest transpire after the study is begun. Huang and Stafford used survey data from the National Ambulatory Medical Care Survey to examine the relationship between demographics and clinical characteristics of women who visit primary care physicians and specialists for urinary tract infection.
Cohort studies often examine what happens to the disease over time—the natural history of the disease. Fifty-one patients undergoing cholecystectomy were evaluated before.
Interviews are sometimes used in surveys. A presenting problem in Chapters 5 describes a cohort study to determine the effect of cholecystectomy on bowel habits and bile acid absorption Sauter et al. As an illustration. Using preexisting databases can have a number of advantages. Kendler and colleagues wanted to investigate the role of genetic and environmental risk factors for substance abuse. Figure illustrates the study design. Typical Cohort Studies A classical cohort study with which most of you are probably familiar is the Framingham study of cardiovascular disease.
Researchers select subjects at the onset of the study and then determine whether they have the risk factor or have been exposed. More than citizens in Framingham. Diermayer and colleagues After interviewing almost sets of adult male twins.
The authors had expected the level of moral reasoning to increase. Many studies have been based on the Framingham cohort. Many journal articles have been written about this cohort. They studied six classes of illicit substances to learn whether substance use disorders are substance-specific. They also sought these other features of an epidemic: This study was begun in to investigate factors associated with the development of atherosclerotic and hypertensive cardiovascular disease.
Many countries and states collect data on a variety of conditions to develop tumor registries and databases of cases of infectious disease. They wanted to learn how moral reasoning progressed over time.
Cohort Studies A cohort is a group of people who have something in common and who remain part of a group over an extended time. Vol 7. Kane provides information on reading outcomes research articles. In a cross-sectional study.
These instruments are commonly called measures of activities of daily living ADL. Lurie and colleagues reported over five-fold variation in rates of advanced spinal imaging across geographic areas.
Different rates of spinal imaging. The reasons for the increase in patient-focused health outcomes are complex. Santora and colleagues studied variations in breast cancer screening among primary care clinicians by geographic location.
Many instruments used to measure physical functional status have been developed to evaluate the extent of a patient's rehabilitation following injury or illness.
There are many kinds of patient outcomes: Patient outcomes have always been of interest to health care providers. They found that written breast cancer guidelines were used less in suburban and urban areas than in rural areas. Specific focus on the health care organizations reported that poor and elderly patients with chronic illnesses had worse outcomes in health maintenance organizations HMO systems than with fee-for-service systems and recommended that health care plans carefully monitor patient outcomes Ware et al.
The group receiving the new program gained significantly more weight from baseline at both the 3-month and 6-month measurements. Quality of life QOL is a broadly defined concept that includes subjective or objective judgments about all aspects of an individual's existence: QOL measures can help determine a patient's preferences for different health states and are often used to help decide among alternative approaches to medical management Wilson and Cleary.
Examples include time spent in the office waiting for the doctor and waiting for resolution after being seen. Other studies focus on variation in resource use among different medical specialties and systems of health care.
Subjects eligible for Meals-on-Wheels were randomized to receive either the traditional program of five hot meals per week. Schematic diagram of cohort study design. Patient satisfaction with medical care is influenced by a number of factors. Some researchers subdivide functional status into physical. The 6-min walk test how far a person can walk in 6 min was studied by Enright and colleagues Interest in measuring QOL was heightened when researchers realized that living a long time does not necessarily imply living a good life.
Patient satisfaction has been discussed for many years and has been shown to be highly associated with whether patients remain with the same physician provider and the degree to which they adhere to their treatment plan Weingarten et al. There continues to be a growing focus on the ways in which patients view and value their health.
Kretser and colleagues used the activities of daily living ADL to compare with models of nutritional intervention. Prospective studies. Many subsequent studies looked at variations in outcomes in different geographic locations or among different ethnic groups that might result from access issues. Comparison of Case—Control and Cohort Studies Both case—control and cohort studies evaluate risks and causes of disease.
This approach to a study is possible if the records on follow-up are complete and adequately detailed and if the investigators can ascertain the current status of the patients. Using standard methods. Studies that merely describe an investigator's experience with a group of patients and attempt to identify features associated with a good or bad outcome fall into this category. The figure shows the timing of surveys. For quality of life.
Shaded areas represent subjects exposed to the antecedent file: Cost-effectiveness and cost—benefit analysis are methods used to evaluate economic outcomes of interventions or different modes of treatment.
Note that the direction of the inquiry is still forward in time. Some outcome studies address a whole host of topics. The journal Medical Care is devoted exclusively to outcome studies. Historical Cohort Studies Many cohort studies are prospective. Cramer and Spilker provide a broad overview of approaches to QOL assessment.
Cost-effectiveness analysis gives policy makers and health providers critical data needed to make informed judgments about interventions Gold et al.
A large number of questionnaires or instruments have been developed to measure outcomes. Brown The time relationship among the different observation study designs is illustrated in Figure Six medical centers had consistently followed a group of patients who had previously been treated with this therapy. One can also undertake a cohort study by using information collected in the past and kept in records or files.
The 36 items are combined to produce a patient profile on eight concepts in addition to summary physical and mental health measures. Many instruments are problem-specific. Shipley and his coinvestigators wanted to assess study outcomes in men with prostate cancer treated with a specific type of radiation therapy see Chapter 4. Shipley used existing records to look at survival and tumor recurrence in men who were treated between and and had had at least four prostate-specific antigen measurements after radiation.
As efforts continue to contain costs of medical care while maintaining a high level of patient care. Schematic diagram of historical cohort study design. The SF provides a way to collect valid data and does not require very much time to complete. Generally speaking. The best way to ensure that the groups are treated similarly is to plan interventions for both groups for the same time period in the same study.
Henderson and colleagues undertook a cohort study to look at the risk factors for depression in the elderly. Table 2 -1 indicates that clinical trials fall into two categories: Authors of medical journal articles reporting experimental studies tend to state explicitly the type of study design used more often than do authors reporting observational studies.
To reduce the chances that subjects or investigators see what they expect to see. The experimental and control groups should be treated alike in all ways except for the procedure itself so that any differences between the groups will be due to the procedure and not to other factors. Schematic diagram of the time relationship among different observational study designs.
As this illustration shows. Controlled trials are studies in which the experimental drug or procedure is compared with another drug or procedure. A comprehensive discussion and illustration of the standard is given by Altman and colleagues Experimental studies in medicine that involve humans are called clinical trials because their purpose is to draw conclusions about a particular procedure or treatment.
A large number of possible biasing factors can play a role in case—control studies. They can be completed in a much shorter time than cohort studies and are correspondingly less expensive to undertake. Trials with Independent Concurrent Controls One way a trial can be controlled is to have two groups of subjects: In some unusual situations.
Methods for file: The investigators could have designed a case—control study had they asked the research question as: Blindedness is discussed in detail in Chapter In spite of their shortcomings with respect to establishing causality. After an initial interview to collect information on potential risk factors.
Uncontrolled trials are studies in which the investigators' experience with the experimental drug or procedure is described. Case—control studies are especially useful for studying rare conditions or diseases that may not manifest themselves for many years. The arrows represent the direction of the inquiry. When only the subject is unaware. In this way.
Another issue is how to assign some patients to the experimental condition and others to the control condition. Because the purpose of an experiment is to determine whether the intervention treatment makes a difference.
We discuss several randomized trials as presenting problems. Chapter 6 presenting problem. One purpose was to learn whether aspirin in low doses reduces the mortality rate from cardiovascular disease.
Participants in this clinical trial were over Randomized Controlled Trials The randomized controlled trial is the epitome of all research designs because it provides the strongest evidence for concluding causation.
This design is not as subject to bias as a study in which patients are treated without regard to any plan. This investigator enrolled the first 40 women who met the inclusion criteria in the group treated in the usual manner no anesthetic block before cryosurgery and enrolled the next 45 women in the group receiving the paracervical block.
Studies using nonrandomized controls are considered to be much weaker because they do nothing to prevent bias in patient assignment. These studies are similar to cohort studies except for the intervention or treatment that is involved. Follow-up occurred 1 and 3 months after cholecystectomy to detect changes such as abdominal pain. This type of study uses patients as their own controls and is called a self-controlled study. Trials with Self-Controls A moderate level of control can be obtained by using the same group of subjects for both experimental and control options.
Schematic diagram of randomized controlled trial design. Studies that do not use randomized assignment are generally referred to as nonrandomized trials or simply as clinical trials or comparative studies. Results indicated that a diet with a normal amount of calcium but reduced animal protein and salt is more effective than the traditional low-calcium diet in reducing the risk of recurrent stones in men with hypercalciuria.
Many investigators believe that studies with nonrandomized controls are open to so many sources of bias that their conclusions are highly questionable. Shaded areas represent subjects assigned to the treatment condition. Nonrandomized Trials Subjects are not always randomized to treatment options.
Although that may not have been true in this study. The primary outcome was the time to the first recurrence of a symptomatic or presence of a radiographically identified stone.
Whenever patients are assigned to treatments within big blocks of time. Borghi and colleagues compared a traditional low-calcium diet with a diet containing a normal amount of calcium but reduced amount of animal protein and salt for the prevention of recurrent kidney stone formation.
An example is a nonrandomized study of the use of a paracervical block to diminish cramping and pain associated with cryosurgery for cervical neoplasia Harper. The study by Sauter and colleagues involved patients who underwent cholecystectomy.
Trials with External Controls The third method for controlling experiments is to use controls external to the study. The groups are then given the alternative treatment. This design uses two groups of patients: One group is assigned to the experimental treatment. The study design is illustrated in Figure In studies involving historical controls. Uncontrolled Studies Not all studies involving interventions have controls. Schematic diagram of trial with crossover. During the washout period.
This design. This study was an uncontrolled study because there were no comparisons with patients treated in another manner. On other occasions. They found some differences in the probability of long-term survival in patients who had different tumor classification scores scores that measure the P. The investigators wanted to determine the length of time a patient had no recurrence of the tumor as well as how long the patients survived.
Crook and associates a presenting problem in Chapter 9 reported the results of a trial of radiotherapy for prostate carcinoma in which patients were followed for at least 12 and for as long as 70 months. After a time. Historical controls are frequently used to study diseases for which cures do not yet exist and are used in oncology studies.
Metaanalysis is similar to review articles. Another problem is finding a significant difference when it may be unfounded. Causation generally cannot be proved with cohort studies because they are observational and do not involve interventions.
This is one file: Clinical trials in which patients are randomly assigned to different treatments. Extended time periods make such studies costly. Six of eight outcomes they examined showed a significant intervention effect in the observational studies. A number of published articles have shown the tendency for nonrandomized studies. The history of medicine is filled with examples in which one particular treatment is recommended and then discontinued after a controlled clinical trial is undertaken.
Guyatt and colleagues identified 13 randomized trials and 17 observational studies in adolescent pregnancy prevention. Schematic diagram of trial with external controls. Although clinical trials provide the greatest justification for determining causation. Metaanalysis uses published information from other studies and combines the results so as to permit an overall conclusion.
One of the treatments is the experimental condition. Cohort studies that require a long time to complete are especially vulnerable to problems associated with patient follow-up. With diseases that develop over a long period of time or with conditions that occur as a result of long-term exposure to some causative agent. They found 12 randomized trials that had addressed this question and combined the results in a statistical manner to reach an overall conclusion about their effectiveness—mainly that the impregnated catheters appear to be effective in reducing the incidence of infection in high-risk patients.
As a result. The length of time required in a cohort study depends on the problem studied. They also make it difficult for investigators to argue causation because other events occurring in the intervening period may have affected the outcome.
This method is especially appropriate when the studies that have been reported have small numbers of subjects or come to different conclusions.
One significant problem with uncontrolled trials is that unproved procedures and therapies can become established. The investigators wanted to know whether catheters impregnated with antiseptic were effective in preventing catheterrelated bloodstream infection. Veenstra and colleagues a presenting problem in Chapter 10 performed a meta -analysis of infection and central venous catheters. Another potential obstacle to using clinical trials occurs when certain practices become established and accepted by the medical community.
The major shortcoming of such studies is that investigators assume that the procedure used and described is the best one. The control may be a placebo or a sham procedure. Uncontrolled studies are more likely to be used when the comparison involves a procedure than when it involves a drug. In some situations. Clinical trials are the best type of study to use when the objective is to establish the efficacy of a treatment or a procedure. Each study design has certain advantages P.
It is possible to do a meta -analysis of observational studies or experiments. In well-designed cohort studies. Of all study methods. In medical research.
They are also a good choice for someone who needs to complete a clinical research project in a specific amount of time. But as we noted previously. Data availability for case—control studies sometimes requires compromises between what researchers wish to study and what they are able to study. Experiments involving humans are called trials. Cohort studies are best for studying the natural progression of disease or risk factors for disease.
Because of the problems inherent in choosing a control group in a case—control study. Each type of study discussed has advantages and disadvantages. Surveys are generally cross-sectional studies. Most of the voter polls done prior to an election are one-time samplings of a group of citizens. In the Framingham cohort study. The men who were at the upper end of the blood pressure distribution 10 years earlier and who had experienced a larger increase have died in the intervening period.
This belief was based on cross-sectional studies that had shown mean diastolic blood pressure to be approximately 80 mm Hg in all age groups. They are generally the quickest and least expensive studies to undertake and are ideal for investigators who need to obtain some preliminary data prior to writing a proposal for a more complete. One of the greatest problems in a case—control study is selection of an appropriate control group. They are easy to write. Cross-sectional studies are similar to case—control studies in being relatively quick to complete.
The P. In general. A common problem with survey research is obtaining sufficiently large response rates. This apparent contradiction is easier to understand if we consider what happens in an aging cohort. The advantages of case—control studies lead to their disadvantages.
The problem of representative participants is not confined to cross -sectional studies. Experimental studies may also use animals and tissue. He found. We discuss issues with surveys more completely in Chapter One of the authors was involved in a study of elderly burn patients in which the goal was to determine risk factors for survival. The conclusions are therefore based on a subset of people who agree to participate. The cases in a case—control study are relatively easy to identify.
Another issue is the way questions are posed to participants. Well-designed observational studies can provide useful insights on disease causation. Cross-sectional studies provide a snapshot of a disease or condition at one time. Ten years later there is an increase in diastolic pressure.
Grodstein and colleagues reported on the relationship between duration.
Group Exercise. Sagawa and colleagues were interested in the efficacy of sputum cytology in a mass screening program for the early detection of lung cancer.
Khalakdina and colleagues could find no published studies of the risk factors for cryptosporidiosis in immunocompetent adults. Carefully examine the research question and decide which study design would be optimal to answer the question.