This short article gives a brief guide to the different study designs and a (P) from which groups of subjects are studied; Outcomes (O) that are measured. Control Clin Trials. Oct;18(5) The relationship between study design, results, and reporting of randomized clinical trials of HIV infection. Ioannidis. No study design is perfect. Each has strengths and drawbacks. It is important to understand a study's design. By doing this, you can understand the results to.
Results and Study Design
The treatment may be drugs, devices, or procedures studied for diagnostic, therapeutic, or prophylactic effectiveness. Control measures include placebos, active medicines, no-treatment, dosage forms and regimens, historical comparisons, etc. When randomization using mathematical techniques, such as the use of a random numbers table, is employed to assign patients to test or control treatments, the trials are characterized as Randomized Controlled Trials.
Cost-Benefit Analysis - A method of comparing the cost of a program with its expected benefits in dollars or other currency. The benefit-to-cost ratio is a measure of total return expected per unit of money spent. This analysis generally excludes consideration of factors that are not measured ultimately in economic terms. Cost effectiveness compares alternative ways to achieve a specific set of results. Cross-Over Studies - Studies comparing two or more treatments or interventions in which the subjects or patients, upon completion of the course of one treatment, are switched to another.
In the case of two treatments, A and B, half the subjects are randomly allocated to receive these in the order A, B and half to receive them in the order B, A.
A criticism of this design is that effects of the first treatment may carry over into the period when the second is given. Cross-Sectional Studies - Studies in which the presence or absence of disease or other health-related variables are determined in each member of the study population or in a representative sample at one particular time.
Double-Blind Method - A method of studying a drug or procedure in which both the subjects and investigators are kept unaware of who is actually getting which specific treatment. Empirical Research - The study, based on direct observation, use of statistical records, interviews, or experimental methods, of actual practices or the actual impact of practices or policies.
Evaluation Studies - Works consisting of studies determining the effectiveness or utility of processes, personnel, and equipment. Genome-Wide Association Study - An analysis comparing the allele frequencies of all available or a whole genome representative set of polymorphic markers in unrelated patients with a specific symptom or disease condition, and those of healthy controls to identify markers associated with a specific disease or condition.
Logistic Models - Statistical models which describe the relationship between a qualitative dependent variable that is, one which can take only certain discrete values, such as the presence or absence of a disease and an independent variable. A common application is in epidemiology for estimating an individual's risk probability of a disease as a function of a given risk factor. Longitudinal Studies - Studies in which variables relating to an individual or group of individuals are assessed over a period of time.
Lost to Follow-Up - Study subjects in cohort studies whose outcomes are unknown e. Matched-Pair Analysis - A type of analysis in which subjects in a study group and a comparison group are made comparable with respect to extraneous factors by individually pairing study subjects with the comparison group subjects e. Meta-Analysis - Works consisting of studies using a quantitative method of combining the results of independent studies usually drawn from the published literature and synthesizing summaries and conclusions which may be used to evaluate therapeutic effectiveness, plan new studies, etc.
It is often an overview of clinical trials. It is usually called a meta-analysis by the author or sponsoring body and should be differentiated from reviews of literature.
Numbers Needed To Treat - Number of patients who need to be treated in order to prevent one additional bad outcome. It is the inverse of Absolute Risk Reduction. Odds Ratio - The ratio of two odds. The exposure-odds ratio for case control data is the ratio of the odds in favor of exposure among cases to the odds in favor of exposure among noncases. The disease-odds ratio for a cohort or cross section is the ratio of the odds in favor of disease among the exposed to the odds in favor of disease among the unexposed.
The prevalence-odds ratio refers to an odds ratio derived cross-sectionally from studies of prevalent cases. Patient Selection - Criteria and standards used for the determination of the appropriateness of the inclusion of patients with specific conditions in proposed treatment plans and the criteria used for the inclusion of subjects in various clinical trials and other research protocols. Predictive Value of Tests - In screening and diagnostic tests, the probability that a person with a positive test is a true positive i.
Predictive value is related to the sensitivity and specificity of the test. Prospective Studies - Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group. Qualitative Studies - Research that derives data from observation, interviews, or verbal interactions and focuses on the meanings and interpretations of the participants. Quantitative Studies - Quantitative research is research that uses numerical analysis.
Random Allocation - A process involving chance used in therapeutic trials or other research endeavor for allocating experimental subjects, human or animal, between treatment and control groups, or among treatment groups. It may also apply to experiments on inanimate objects.
Randomized Controlled Trial - Clinical trials that involve at least one test treatment and one control treatment, concurrent enrollment and follow-up of the test- and control-treated groups, and in which the treatments to be administered are selected by a random process, such as the use of a random-numbers table.
Reproducibility of Results - The statistical reproducibility of measurements often in a clinical context , including the testing of instrumentation or techniques to obtain reproducible results.
The concept includes reproducibility of physiological measurements, which may be used to develop rules to assess probability or prognosis, or response to a stimulus; reproducibility of occurrence of a condition; and reproducibility of experimental results. Retrospective Studies - Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past.
The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons. Sample Size - The number of units persons, animals, patients, specified circumstances, etc.
The sample size should be big enough to have a high likelihood of detecting a true difference between two groups. Sensitivity and Specificity - Binary classification measures to assess test results. Sensitivity or recall rate is the proportion of true positives. Specificity is the probability of correctly determining the absence of a condition. Single-Blind Method - A method in which either the observer s or the subject s is kept ignorant of the group to which the subjects are assigned.
Time Factors - Elements of limited time intervals, contributing to particular results or situations. Search this Guide Search. Types of Clinical Study Designs This interdisciplinary guide describes the basic steps of doing a literature review.
Introduction Toggle Dropdown Library Basics 1. See also Levels of Evidence. Figure 1 shows the tree of possible designs, branching into subgroups of study designs by whether the studies are descriptive or analytic and by whether the analytic studies are experimental or observational.
The list is not completely exhaustive but covers most basics designs. Tree of different types of studies Q1, 2, and 3 refer to the three questions below.
Our first distinction is whether the study is analytic or non-analytic. A non-analytic or descriptive study does not try to quantify the relationship but tries to give us a picture of what is happening in a population, e.
Descriptive studies include case reports, case-series, qualitative studies and surveys cross-sectional studies, which measure the frequency of several factors, and hence the size of the problem. An analytic study attempts to quantify the relationship between two factors, that is, the effect of an intervention I or exposure E on an outcome O. To quantify the effect we will need to know the rate of outcomes in a comparison C group as well as the intervention or exposed group.
Whether the researcher actively changes a factor or imposes uses an intervention determines whether the study is considered to be observational passive involvement of researcher , or experimental active involvement of researcher. In experimental studies, the researcher manipulates the exposure, that is he or she allocates subjects to the intervention or exposure group.
Experimental studies, or randomised controlled trials RCTs , are similar to experiments in other areas of science. That is, subjects are allocated to two or more groups to receive an intervention or exposure and then followed up under carefully controlled conditions. Such studies controlled trials, particularly if randomised and blinded, have the potential to control for most of the biases that can occur in scientific studies but whether this actually occurs depends on the quality of the study design and implementation.
In analytic observational studies, the researcher simply measures the exposure or treatments of the groups. These studies all include matched groups of subjects and assess of associations between exposures and outcomes. Observational studies investigate and record exposures such as interventions or risk factors and observe outcomes such as disease as they occur.
Such studies may be purely descriptive or more analytical.
Design & Sample
The design of experiments is the design of any .. What is the influence of delayed effects of substantive factors on outcomes? How do response shifts affect self-report. A High quality: Consistent, generalizable results; sufficient sample size for the study design; adequate control; definitive conclusions; consistent. The primary outcomes are not measured in living human subjects. Case series are a commonly reported study design, but the label "case series" is rarely.