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Observational Study

A type of study in which individuals are observed or certain outcomes are measured. No attempt is made to affect the outcome.

PubMed Health Glossary
(Source: NIH - National Cancer Institute)

About Observational Studies

In an observational uncontrolled study, researchers simply watch what happens to a series of people in one group. For example, everyone gets drug X, and the researchers record how many people get better. But there's a big problem with these studies: you can't know what would have happened without drug X - maybe more people would have gotten better!

Whenever you hear the results of a study about how well an intervention works, ask whether the study included a control group (a group of people who did not undergo the intervention). Without a control group, it's impossible to know whether the intervention really accounts for the study findings. Remind yourself that, no matter how dramatically the findings from an uncontrolled study are described, they are not particularly believable.

Stronger scientific evidence comes from controlled studies, in which researchers watch what happens to different groups of people. The most basic kinds of controlled studies involve observational research, in which the researchers merely record what happens to people in different situations, without intervening. Cohort and case-control studies are perhaps the best-known types of observational controlled research.

Such research first linked cigarette smoking to lung cancer, and high cholesterol to heart disease. This is the only way to study dangerous exposures. But these kinds of studies have important problems. Although they can show that an intervention is associated with a particular outcome, they cannot by themselves prove that the intervention causes the outcome. It's always possible that other factors not accounted for in the research are causing the outcome.

For example, researchers might believe that eating string beans prevents heart attacks. To test this hypothesis, they compare people who eat a lot of string beans with people who never eat string beans to see which group has more heart attacks. Of course, these groups of people may be very different in lots of ways besides eating string beans. For instance, let's say that people who choose to eat string beans might be more likely to be vegetarians, to eat a Mediterranean diet, and to exercise. So if the string bean eaters "do better" than the others, it might not be because of the string beans.
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Articles on this research topic

PubMed Health

Comparing effect estimates of randomized controlled trials and observational studies

Researchers and organizations often use evidence from randomized controlled trials (RCTs) to determine the efficacy of a treatment or intervention under ideal conditions, while studies of observational designs are used to measure the effectiveness of an intervention in non‐experimental, 'real world' scenarios. Sometimes, the results of RCTs and observational studies addressing the same question may have different results. This review explores the questions of whether these differences in results are related to the study design itself, or other study characteristics.

Assessing Risk of Bias and Confounding in Observational Studies of Interventions or Exposures: Further Development of the RTI Item Bank [Internet]

To develop a framework for the assessment of the risk of bias and confounding against causality from a body of observational evidence, and to refine a tool to aid in identifying risk of bias, confounding, and precision in individual studies.

Can valid and practical risk-prediction or casemix adjustment models, including adjustment for comorbidity, be generated from English hospital administrative data (Hospital Episode Statistics)? A national observational study

The study found that casemix adjustment models can be derived from HES data using logistic regression, and that machine learning methods are more difficult to use and provide little better results with these data.

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Terms to know

Case-Control Study
A study that compares two groups of people: those with the disease or condition under study (cases) and a ver...
Cohort
A group of individuals who share a common trait, such as birth year. In medicine, a cohort is a group that is...
Cohort Study
A research study that compares a particular outcome (such as lung cancer) in groups of individuals who are al...
Cross-Sectional Study
A cross-sectional study is a type of observational study that involves the analysis of data collected from a...
Epidemiology
The study of the patterns, causes, and control of disease in groups of people....
Longitudinal Study
Investigation in which data are collected from a number of people over a long period of time....

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Terms to know

Case-Control Study
A study that compares two groups of people: those with the disease or condition under study (cases) and a ver...
Cohort
A group of individuals who share a common trait, such as birth year. In medicine, a cohort is a group that is...
Cohort Study
A research study that compares a particular outcome (such as lung cancer) in groups of individuals who are al...
See all 6

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