Clinical study design is the formulation of trials and experiments in medical and epidemiological research, sometimes known as clinical trial

Clinical trial

Clinical trials are a set of procedures in medical research and drug development that are conducted to allow safety and efficacy data to be collected for health interventions...

s. Many of the considerations here are shared under the more general topic of design of experiments

Design of experiments

In general usage, design of experiments or experimental design is the design of any information-gathering exercises where variation is present, whether under the full control of the experimenter or not. However, in statistics, these terms are usually used for controlled experiments...

 but there can be others, in particular related to patient confidentiality and ethics.

Treatment studies

• Randomized controlled trial
  Randomized controlled trial
  A randomized controlled trial is a type of scientific experiment - a form of clinical trial - most commonly used in testing the safety and efficacy or effectiveness of healthcare services or health technologies A randomized controlled trial (RCT) is a type of scientific experiment - a form of...
  
  
  • Double-blind randomized trial
  • Single-blind randomized trial
  • Non-blind trial
    Open-label trial
    An open-label trial or open trial is a type of clinical trial in which both the researchers and participants know which treatment is being administered....
    
    
• Nonrandomized trial
  Quasi-experimental design
  The design of a quasi-experiment relates to a particular type of experiment or other study in which one has little or no control over the allocation of the treatments or other factors being studied. The key difference in this empirical approach is the lack of random assignment...
  
   (quasi-experiment)
  • Interrupted time series design (measures on a sample or a series of samples from the same population are obtained several times before and after a manipulated event or a naturally occurring event) - considered a type of quasi-experiment

Observational studies

• Cohort study
  Cohort study
  A cohort study or panel study is a form of longitudinal study used in medicine, social science, actuarial science, and ecology. It is an analysis of risk factors and follows a group of people who do not have the disease, and uses correlations to determine the absolute risk of subject contraction...
  
  
  • Prospective cohort
    Prospective cohort study
    A prospective cohort study is a cohort study that follows over time a group of similar individuals who differ with respect to certain factors under study, to determine how these factors affect rates of a certain outcome...
    
    
  • Retrospective cohort
    Retrospective cohort study
    A retrospective cohort study, also called a historic cohort study, generally means to take a look back at events that already have taken place...
    
    
  • Time series study
    Time series
    In statistics, signal processing, econometrics and mathematical finance, a time series is a sequence of data points, measured typically at successive times spaced at uniform time intervals. Examples of time series are the daily closing value of the Dow Jones index or the annual flow volume of the...
    
    
• Case-control study
  Case-control
  A case-control study is a type of study design in epidemiology. Case-control studies are used to identify factors that may contribute to a medical condition by comparing subjects who have that condition with patients who do not have the condition but are otherwise similar .Case-control studies are...
  
  
  • Nested case-control study
    Nested case-control study
    A nested case control study is a variation of a case-cohort study in which only a subset of controls from the cohort are compared to the incident cases. In a case-cohort study, all incident cases in the cohort are compared to a random subset of participants who do not develop the disease of interest...
    
    
• Cross-sectional study
  Cross-sectional study
  Cross-sectional studies form a class of research methods that involve observation of all of a population, or a representative subset, at one specific point in time...
  
  
  • Community survey (a type of cross-sectional study)
• Ecological study
  Ecological study
  An ecological study is an epidemiological study in which the unit of analysis is a population rather than an individual. For instance, an ecological study may look at the association between smoking and lung cancer deaths in different countries...
  
  

Important considerations

When choosing a study design, many factors must be taken into account. Different types of studies are subject to different types of bias. For example, recall bias is likely to occur in cross-sectional or case-control studies where subjects are asked to recall exposure to risk factors. Subjects with the relevant condition (e.g. breast cancer) may be more likely to recall the relevant exposures that they had undergone (e.g. hormone replacement therapy) than subjects who don't have the condition.

The ecological fallacy

Ecological fallacy

An ecological fallacy is a logical fallacy in the interpretation of statistical data in an ecological study, whereby inferences about the nature of specific individuals are based solely upon aggregate statistics collected for the group to which those individuals belong...

 may occur when conclusions about individuals are drawn from analyses conducted on grouped data. The nature of this type of analysis tends to overestimate the degree of association between variables.

Seasonal studies

Conducting studies in seasonal indications (such as allergies, Seasonal Affective Disorder

Seasonal affective disorder

Seasonal affective disorder , also known as winter depression, winter blues, summer depression, summer blues, or seasonal depression, is a mood disorder in which people who have normal mental health throughout most of the year experience depressive symptoms in the winter or summer, spring or autumn...

, influenza

Influenza

Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...

, and others) can complicate a trial as patients must be enrolled quickly. Additionally, seasonal variations and weather patterns can effect a seasonal study.

Other terms

• The term retrospective study is sometimes used as another term for a case-control study. This use of the term "retrospective study" is misleading, however, and should be avoided because other research designs besides case-control studies are also retrospective in orientation.
• Superiority trials are designed to demonstrate that one treatment is more effective than another.
• Non-inferiority trials are designed to demonstrate that a treatment is at least not appreciably worse than another.
• Equivalence trials are designed to demonstrate that one treatment is as effective as another.
• When using "parallel groups", each patient receives one treatment; in a "crossover study
  Crossover study
  A crossover study is a longitudinal study in which subjects receive a sequence of different treatments . While crossover studies can be observational studies, many important crossover studies are controlled experiments, which are discussed in this article...
  
  ", each patient receives several treatments.
• A longitudinal study
  Longitudinal study
  A longitudinal study is a correlational research study that involves repeated observations of the same variables over long periods of time — often many decades. It is a type of observational study. Longitudinal studies are often used in psychology to study developmental trends across the...
  
   research subjects over two or more points in time; by contrast, while a cross-sectional study
  Cross-sectional study
  Cross-sectional studies form a class of research methods that involve observation of all of a population, or a representative subset, at one specific point in time...
  
   assesses research subjects at one point in time.

See also

• Conceptual framework
  Conceptual framework
  A conceptual framework is used in research to outline possible courses of action or to present a preferred approach to an idea or thought. For example, the philosopher Isaiah Berlin used the "hedgehogs" versus "foxes" approach; a "hedgehog" might approach the world in terms of a single organizing...
  
  
• Epidemiological methods
  Epidemiological methods
  The science of epidemiology has matured significantly from the times of Hippocrates and John Snow. The techniques for gathering and analyzing epidemiological data vary depending on the type of disease being monitored but each study will have overarching similarities....
  
  
• Experimental control
• Meta-analysis
  Meta-analysis
  In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. In its simplest form, this is normally by identification of a common measure of effect size, for which a weighted average might be the output of a meta-analyses. Here the...
  
  
• Operationalization
  Operationalization
  In humanities, operationalization is the process of defining a fuzzy concept so as to make the concept clearly distinguishable or measurable and to understand it in terms of empirical observations...
  
  

External links

• Epidemiologic.org Epidemiologic Inquiry online weblog for epidemiology researchers
• Epidemiology Forum An epidemiology discussion and forum community to foster debates and collaborations in epidemiology
• Some aspects of study design Tufts University web site
• Comparison of strength Description of study designs from the National Cancer Institute
• Political Science Research Design Handbook Truman State University website