Study Designs. This short article gives a brief guide to the different study types and a comparison of the advantages and disadvantages. See also Levels of. Clinical study design is the formulation of trials and experiments, as well as observational studies in medical, clinical and other types of research (e.g. The design of any study is more important than analyzing its results, as a poorly designed study can never be recovered, whereas a poorly.
Of course, we always try to use the best possible design, but sometimes this is not practical or ethically acceptable you cannot do an experiment to expose some people to a harmful substance to see what effect it has. Therefore, you need to understand the strengths and limitations of each type of study design, as applied to a particular research purpose. The purposes we will consider include 1 describing the prevalence of health problems; 2 identifying causes of health problems etiological research , and 3 evaluating therapy, including treatment and prevention.
First, distinguish between observational and experimental studies. In observational studies, the researcher observes and systematically collects information, but does not try to change the people or animals, or reagents being observed. In an observational study there is no intervention. When you merely want to collect descriptive information: When you want to report on the causes of a problem without disturbing the natural setting I want to find out why students do not attend lectures.
When you can't do an experiment: When it's not acceptable to do an experiment: What types of observational study are there? Lots, but you need to know about three main ones:. Here, you draw a random sample of people and record information about their health in a systematic manner. You can also compare people with, and without, diabetes in terms of characteristics such as being overweight that may be associated with the disease. The problem is that you cannot be sure which came first: These are like surveys, but extend over time.
This allows you to study changes and to establish the time-sequence in which things occur. Therefore, you can use this to study causes.
For example, you could draw a sample of people medical students, for example who do not have the disease you are interested in, and collect information on the factor you have hypothesized to be a cause of the disease. Maybe you want to see whether using a cell phone leads to brain cancer. So, collect information on how many minutes each student uses their phone each week you might get permission to obtain this from their phone company bills , and collect this information over a long time, and then eventually collect information on who gets brain cancer.
You could then see whether the cases of brain cancer arose among the people who used their cell phones most often. There are various methods to randomize study participants to their groups. Meditation or exercise for preventing acute respiratory infection: Barrett B, et al. Cohort Study Prospective Observational Study A clinical research study in which people who presently have a certain condition or receive a particular treatment are followed over time and compared with another group of people who are not affected by the condition.
Smokeless tobacco cessation in South Asian communities: Croucher R, et al. Case-control Study Case-control studies begin with the outcomes and do not follow people over time. Researchers choose people with a particular result the cases and interview the groups or check their records to ascertain what different experiences they had. They compare the odds of having an experience with the outcome to the odds of having an experience without the outcome.
Non-use of bicycle helmets and risk of fatal head injury: Persaud N, et al. Cross-sectional study The observation of a defined population at a single point in time or time interval. Exposure and outcome are determined simultaneously.
Fasting might not be necessary before lipid screening: Steiner MJ, et al. Case Reports and Series A report on a series of patients with an outcome of interest. No control group is involved. Students mentoring students in a service-learning clinical supervision experience: Lattanzi JB, et al.
Ideas, Editorials, Opinions Put forth by experts in the field. Health and health care for the 21st century: Am J Public Health. Animal Research Studies Studies conducted using animal subjects. Intranasal leptin reduces appetite and induces weight loss in rats with diet-induced obesity DIO. Test-tube Lab Research "Test tube" experiments conducted in a controlled laboratory setting. Adapted from Study Designs. Bias - Any deviation of results or inferences from the truth, or processes leading to such deviation.
Bias can result from several sources: There is no sense of prejudice or subjectivity implied in the assessment of bias under these conditions. Case Control Studies - Studies which start with the identification of persons with a disease of interest and a control comparison, referent group without the disease. The relationship of an attribute to the disease is examined by comparing diseased and non-diseased persons with regard to the frequency or levels of the attribute in each group.
Causality - The relating of causes to the effects they produce. Causes are termed necessary when they must always precede an effect and sufficient when they initiate or produce an effect.
Any of several factors may be associated with the potential disease causation or outcome, including predisposing factors, enabling factors, precipitating factors, reinforcing factors, and risk factors. In an experimental study a population is selected to receive a specific intervention the effects of which are measured by comparing the outcomes in the experimental group with the outcomes of a control group that has received another intervention or placebo.
Examples include randomized controlled trial, cluster randomized controlled trial, nonrandomized trial, n-of-one trial. See also observational study. The simplest form of observational study is the case report or case series, which describes the clinical course of individuals with a particular condition or diagnosis.
Observational studies include descriptive and analytic studies. See also experimental study. A type of study in which the investigator s evaluates the effect of an intervention but does not have full control over the timing, course, or allocation of the intervention. They are often used when it is not possible to conduct a true experimental study.
Turn recording back on. National Center for Biotechnology Information , U. Appendix B Taxonomy on Study Design. Study Design Key Below is a list of definitions that correlate with study designs assigned by the accompanying taxonomy. Non-randomized trial A study in which individuals or groups of individuals e. Randomized trial A study designed to test the efficacy of an intervention on an individual, a group of individuals, or clusters e.
Prospective cohort study A study in which individuals in the group without the outcome s of interest e. Retrospective cohort study A study in which a group of individuals is identified on the basis of common features that were determined in the past. Controlled before-after study A study in which the outcome s of interest is measured both before and after the intervention or exposure in two or more groups of individuals.
Non-concurrent cohort study A study in which 2 or more groups of individuals are identified on the basis of common features at different time points. Nested case control study A study where exposed and control subjects are drawn from the population of a prospective cohort study.
Case control study A study in which participants are selected based on the known outcome s of interest e. Before-after study A study of an intervention or exposure in which the investigator s compares the outcome s of interest both before and after the intervention in the same group of individuals. Cross-sectional study A study in which both the exposure and the outcome status in a target population are assessed concurrently, that is, at the same point in time or during a brief period of time.
Non-comparative study case series Examples of this design include: Cluster randomized controlled trial Synonym: Experimental study A type of study in which investigators have direct control over the timing, course, and assignment of the intervention. Quasi-experimental study A type of study in which the investigator s evaluates the effect of an intervention but does not have full control over the timing, course, or allocation of the intervention.
Clinical study design
Meta-Analysis A way of combining data from many different research studies. A meta-analysis is a statistical process that combines the findings. The evidence for evidence-based medicine is all collected via research, which uses a variety of study designs. You will be learning about "critical appraisal of. Statistics is all about forming questions and gathering data to explore those questions. This unit covers sampling and survey methods, observational studies, and.