Observational study

observational studiesobservationalobservational dataexaminationnon-experimentalstudydescriptivefield observationsobservationobservational clinical trials
In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concerns or logistical constraints.wikipedia
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Statistics

statisticalstatistical analysisstatistician
In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concerns or logistical constraints.
In contrast, an observational study does not involve experimental manipulation.

Case–control study

case-control studiescase-controlcase-control study
A case–control study (also known as case–referent study) is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute.

Longitudinal study

longitudinal studieslongitudinallongitudinal research
It is often a type of observational study, although they can also be structured as longitudinal randomized experiments.

Cross-sectional study

cross-sectionalcross-sectional studiescross-sectional analysis
In medical research, social science and biology, a cross-sectional study (also known as a cross-sectional analysis, transverse study, prevalence study) is a type of observational study that analyzes data from a population, or a representative subset, at a specific point in time—that is, cross-sectional data.

Psychology

psychologicalpsychologistpsychologists
In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concerns or logistical constraints.
Observational studies analyze uncontrolled data in search of correlations; multivariate statistics are typically used to interpret the more complex situation.

Randomized controlled trial

randomized controlled trialsrandomized clinical trialrandomized control trial
This is in contrast with experiments, such as randomized controlled trials, where each subject is randomly assigned to a treated group or a control group. A report from the Cochrane Collaboration in 2014 came to the conclusion that observational studies are very similar in results reported by similarly conducted randomized controlled trials.
Two studies published in The New England Journal of Medicine in 2000 found that observational studies and RCTs overall produced similar results.

Matching (statistics)

matchingmatchedOvermatching
In healthcare and the social sciences, investigators may use matching to compare units that nonrandomly received the treatment and control.
Matching is a statistical technique which is used to evaluate the effect of a treatment by comparing the treated and the non-treated units in an observational study or quasi-experiment (i.e. when the treatment is not randomly assigned).

Propensity score matching

Propensity scorematched sample estimationPropensity Score Watching
One common approach is to use propensity score matching in order to reduce confounding.
In the statistical analysis of observational data, propensity score matching (PSM) is a statistical matching technique that attempts to estimate the effect of a treatment, policy, or other intervention by accounting for the covariates that predict receiving the treatment.

Experiment

experimentalexperimentationexperiments
This is in contrast with experiments, such as randomized controlled trials, where each subject is randomly assigned to a treated group or a control group.
An observational study is used when it is impractical, unethical, cost-prohibitive (or otherwise inefficient) to fit a physical or social system into a laboratory setting, to completely control confounding factors, or to apply random assignment.

Natural experiment

natural experimentsnaturalexperimental variable
Thus, natural experiments are observational studies and are not controlled in the traditional sense of a randomized experiment.

Cochrane (organisation)

Cochrane reviewCochrane CollaborationCochrane
A report from the Cochrane Collaboration in 2014 came to the conclusion that observational studies are very similar in results reported by similarly conducted randomized controlled trials.
A few reviews, in occupational health for example, incorporate results from non-randomised observational studies, as well as controlled before–after (CBA) studies and interrupted time-series studies.

Strengthening the reporting of observational studies in epidemiology

STROBE
In 2007, several prominent medical researchers issued the Strengthening the reporting of observational studies in epidemiology (STROBE) statement, in which they called for observational studies to conform to 22 criteria that would make their conclusions easier to understand and generalise.
The STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) Statement is a reporting guideline including a checklist of 22 items that are considered essential for good reporting of observational studies.

Difference in differences

difference-in-differencesdifference-in-differenceAssumptions
Difference in differences (DID or DD ) is a statistical technique used in econometrics and quantitative research in the social sciences that attempts to mimic an experimental research design using observational study data, by studying the differential effect of a treatment on a 'treatment group' versus a 'control group' in a natural experiment.

Confounding

confounding factorconfounding variableconfounding variables
One common approach is to use propensity score matching in order to reduce confounding.
In epidemiology, one type is "confounding by indication", which relates to confounding from observational studies.

Epidemiology

epidemiologistepidemiologicalepidemiologists
In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concerns or logistical constraints.

Social science

social sciencessocial scientistsocial
In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concerns or logistical constraints. In healthcare and the social sciences, investigators may use matching to compare units that nonrandomly received the treatment and control.

Sample (statistics)

samplesamplesstatistical sample
In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concerns or logistical constraints.

Statistical population

populationsubpopulationsubpopulations
In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concerns or logistical constraints.

Dependent and independent variables

dependent variableindependent variableexplanatory variable
In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concerns or logistical constraints.

Scientific control

controlcontrolscontrolled
In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concerns or logistical constraints.

Treatment and control groups

control groupcontrol groupstreatment group
One common observational study is about the possible effect of a treatment on subjects, where the assignment of subjects into a treated group versus a control group is outside the control of the investigator.

Random assignment

randomly assignedrandomizationassignment of treatments to units
This is in contrast with experiments, such as randomized controlled trials, where each subject is randomly assigned to a treated group or a control group.

Abortion–breast cancer hypothesis

link between abortion and breast cancerabortion and breast cancerabortion – breast cancer hypothesis