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The introduction to this article provides insufficient context for those unfamiliar with the subject. Please help improve the article with a good introductory style. (March 2010) Clinical study design is the formulation of trials and experiments in medical and epidemiological research, sometimes known as clinical trials. Many of the considerations here are shared under the more general topic of design of experiments but there can be others, in particular related to patient confidentiality and ethics. Contents 1 Outline of types of designs for clinical studies 1.1 Treatment studies 1.2 Observational studies 2 Important considerations 2.1 Seasonal studies 3 Other terms 4 See also 5 External links 6 References // Outline of types of designs for clinical studies Treatment studies Randomized controlled trial Double-blind randomized trial Single-blind randomized trial Non-blind trial Nonrandomized trial (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 Prospective cohort Retrospective cohort Time series study Case-control study Nested case-control study Cross-sectional study Community survey (a type of cross-sectional study) Ecological study 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 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, influenza, and others) can complicate a trial as patients must be enrolled quickly. Additionally, seasonal variations and weather patterns can effect a seasonal study.[1][2] 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", each patient receives several treatments. A longitudinal study research subjects over two or more points in time; by contrast, while a cross-sectional study assesses research subjects at one point in time. See also Conceptual framework Epidemiological methods Experimental control Meta-analysis Operationalization 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 Study Design Tutorial Cornell University College of Veterinary Medicine References ^ Yamin Khan and Sarah Tilly. "Flu, Season, Diseases Affect Trials". Applied Clinical Trials Online. http://appliedclinicaltrialsonline.findpharma.com/appliedclinicaltrials/Drug+Development/Flu-Season-Diseases-Affect-Trials/ArticleStandard/Article/detail/652128. Retrieved 26 February 2010.  ^ Yamin Khan and Sarah Tilly. "Seasonality: The Clinical Trial Manager's Logistical Challenge". published by: Pharm-Olam International. http://www.pharm-olam.com/pdfs/POI-Seasonality.pdf. Retrieved 26 April 2010.  v • d • e Biomedical research: Clinical study design / Design of experiments Overview Clinical trial · Clinical trial protocol · Clinical trial management · Academic clinical trials Controlled study (EBM I to II-1; A to B) Randomized controlled trial (Blind experiment, Open-label trial) Observational study (EBM II-2 to II-3; B to C) Cross-sectional study vs. Longitudinal study, Ecological study Cohort study (Retrospective cohort study, Prospective cohort study) Case-control study (Nested case-control study) Case series · Case study / Case report Epidemiology/ methods occurrence: Incidence (Cumulative incidence) · Prevalence (Point prevalence, Period prevalence) association: absolute (Absolute risk reduction, Attributable risk, Attributable risk percent) · relative (Relative risk, Odds ratio, Hazard ratio) other: Virulence · Infectivity · Mortality rate · Morbidity · Case fatality · Specificity and sensitivity · Likelihood-ratios Trial/test types In vitro / In vivo · Animal testing · Animal testing on non-human primates · First-in-man study · Multicenter trial · Seeding trial · Vaccine trial Analysis of clinical trials Risk-benefit analysis Interpretation of results Selection bias · Correlation does not imply causation · Null result Category · Glossary · List of topics v • d • e Statistics   Descriptive statistics Continuous data Location Mean (Arithmetic, Geometric, Harmonic) · Median · Mode Dispersion Range  · Standard deviation  · Coefficient of variation  · Percentile  · Interquartile range Shape Variance · Skewness · Kurtosis · Moments · L-moments Count data Index of dispersion Summary tables Grouped data  · Frequency distribution · Contingency table Dependence Pearson product-moment correlation · Rank correlation (Spearman's rho, Kendall's tau) · Partial correlation · Scatter plot Statistical graphics Bar chart · Biplot · Box plot · Control chart · Correlogram · Forest plot · Histogram · Q-Q plot · Run chart · Scatter plot · Stemplot · Radar chart   Data collection Designing studies Effect size  · Standard error  · Statistical power  · Sample size determination Survey methodology Sampling  · Stratified sampling  · Opinion poll · Questionnaire Controlled experiment Design of experiments  · Randomized experiment  · Random assignment  · Replication · Blocking · Regression discontinuity  · Optimal design Uncontrolled studies Natural experiment  · Quasi-experiment  · Observational study   Statistical inference Bayesian inference Bayesian probability  · Prior  · Posterior · Credible interval  · Bayes factor  · Bayesian estimator · Maximum posterior estimator Frequentist inference Confidence interval  · Hypothesis testing  · Sampling distribution  · Meta-analysis Specific tests Z-test (normal) · Student's t-test · F-test · Chi-square test · Pearson's chi-square · Wald test · Mann–Whitney U · Shapiro–Wilk · Signed-rank  · Likelihood-ratio General estimation Mean-unbiased  · Median-unbiased  · Maximum likelihood · Method of moments · Minimum distance · Maximum spacing  · Density estimation   Correlation and regression analysis Correlation Pearson product-moment correlation · Partial correlation · Confounding variable · Coefficient of determination Regression analysis Errors and residuals · Regression model validation  · Mixed effects models · Simultaneous equations models Linear regression Simple linear regression · Ordinary least squares · General linear model · Bayesian regression Non-standard predictors Nonlinear regression · Nonparametric · Semiparametric  · Isotonic  · Robust Generalized linear model Exponential families  · Logistic (Bernoulli)  · Binomial  · Poisson Formal analyses Analysis of variance (ANOVA)  · Analysis of covariance  · Multivariate ANOVA   Data analyses and models for other specific data types Multivariate statistics Multivariate regression · Principal components · Factor analysis · Cluster analysis · Copulas Time series analysis Decomposition · Trend estimation · Box–Jenkins · ARMA models · Spectral density estimation Survival analysis Survival function · Kaplan–Meier · Logrank test · Failure rate · Proportional hazards models · Accelerated failure time model Categorical data McNemar's test · Cohen's kappa   Applications Engineering statistics Methods engineering  · Probabilistic design  · Process & Quality control  · Reliability  · System identification Environmental statistics Geostatistics  · Climatology Medical statistics Epidemiology  · Clinical trial  · Clinical study design Social statistics Actuarial science  · Population  · Demography  · Census  · Psychometrics · Official statistics  · Crime statistics Category · Portal · Outline · Index