Study with uncontrolled variable of interest

Observational study

Observational study

In fields such as <a href="/en/Epidemiology" title="Epidemiology" class="wl">epidemiology</a>, <a href="/en/Social_science" title="Social science" class="wl">social sciences</a>, <a href="/en/Psychology" title="Psychology" class="wl">psychology</a> and <a href="/en/Statistics" title="Statistics" class="wl">statistics</a>, an observational study draws inferences from a <a href="/en/Sample_(statistics)" title="Sample (statistics)" class="mw-redirect wl">sample</a> to a <a href="/en/Statistical_population" title="Statistical population" class="wl">population</a> where the <a href="/en/Dependent_and_independent_variables" title="Dependent and independent variables" class="wl">independent variable</a> is not under the <a href="/en/Scientific_control" title="Scientific control" class="wl">control</a> of the researcher because of ethical concerns or logistical constraints. 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 <a href="/en/Control_group" title="Control group" class="mw-redirect wl">control group</a> is outside the control of the investigator.<a href="#cite_note-urlObservational_study-1" style="counter-reset: mw-Ref 1;">[1]</a><a href="#cite_note-2" style="counter-reset: mw-Ref 2;">[2]</a> This is in contrast with <a href="/en/Experiment" title="Experiment" class="wl">experiments</a>, such as <a href="/en/Randomized_controlled_trial" title="Randomized controlled trial" class="wl">randomized controlled trials</a>, where each subject is <a href="/en/Random_assignment" title="Random assignment" class="wl">randomly assigned</a> to a treated group or a control group. Observational studies, for lacking an assignment mechanism, naturally present difficulties for inferential analysis.

<div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none" about="#mwt1">Study with uncontrolled variable of interest</div>
<figure class="mw-default-size wiki-thumb"><a href="/en/File:Blankett,_Antropoloogiline_vaatlusleht,_vorm_nr._4,_1961.jpg" class="mw-file-description image media-thumb" data-hash="File:Blankett,_Antropoloogiline_vaatlusleht,_vorm_nr._4,_1961.jpg"><img loading="lazy" src="//upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Blankett%2C_Antropoloogiline_vaatlusleht%2C_vorm_nr._4%2C_1961.jpg/220px-Blankett%2C_Antropoloogiline_vaatlusleht%2C_vorm_nr._4%2C_1961.jpg" decoding="async" data-file-width="2446" data-file-height="1680" data-file-type="bitmap" height="151" width="220" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Blankett%2C_Antropoloogiline_vaatlusleht%2C_vorm_nr._4%2C_1961.jpg/330px-Blankett%2C_Antropoloogiline_vaatlusleht%2C_vorm_nr._4%2C_1961.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Blankett%2C_Antropoloogiline_vaatlusleht%2C_vorm_nr._4%2C_1961.jpg/440px-Blankett%2C_Antropoloogiline_vaatlusleht%2C_vorm_nr._4%2C_1961.jpg 2x" alt="Blankett%2C_Antropoloogiline_vaatlusleht%2C_vorm_nr._4%2C_1961.jpg"></a><figcaption>Anthropological survey paper from 1961 by Juhan Aul (<a href="/et/Juhan%20Aul" title="et:Juhan Aul" class="extiw wl">et</a>) from <a href="/en/University_of_Tartu" title="University of Tartu" class="wl">University of Tartu</a> who measured about 50&nbsp;000 people</figcaption></figure>

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. 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. 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. Observational studies, for lacking an assignment mechanism, naturally present difficulties for inferential analysis. 