Statistics

=====Observational study=====
An example of an observational study is one that explores the association between smoking and lung cancer. This type of study typically uses a survey to collect observations about the area of interest and then performs statistical analysis. In this case, the researchers would collect observations of both smokers and non-smokers, perhaps through a [[cohort study]], and then look for the number of cases of lung cancer in each group.<ref>{{cite book|editor1-last=Rothman|editor1-first=Kenneth J|editor2-last=Greenland|editor2-first=Sander|editor3-last=Lash|editor3-first=Timothy|title=Modern Epidemiology|url=https://archive.org/details/modernepidemiolo00roth|url-access=limited|date=2008|publisher=Lippincott Williams & Wilkins|page=[https://archive.org/details/modernepidemiolo00roth/page/n100 100]|edition=3rd|language=en|chapter=7|isbn=978-0781755641}}</ref> A [[case-control study]] is another type of observational study in which people with and without the outcome of interest (e.g. lung cancer) are invited to participate and their exposure histories are collected.