Final answer:
A nested case-control study follows the steps of starting with cases, selecting controls, defining exposures, and collecting data. This method reduces bias and provides a more accurate association between exposures and outcomes within an established cohort.
Step-by-step explanation:
A nested case-control study is a specialized type of case-control study that begins by identifying cases and controls from within a defined cohort. The correct sequence of steps for a nested case-control study is: (a) Starts with cases, selects controls, defines exposures, collects data. Let's walk through these steps:
- First, cases (individuals who have developed the trait of interest or outcome) are identified from within an established cohort.
- Next, controls (individuals without the trait or outcome) are selected from the same cohort and are often matched on various factors like age and gender to the cases.
- Then, exposures or risk factors of interest are defined based on the data already collected or additional data may be gathered.
- Finally, researchers collect and analyze the data to compare exposures between cases and controls to identify potential associations.
By conducting the study in this manner, researchers can control for confounders and reduce recall bias since the data on exposure predates the development of the outcome. This is an important aspect when we compare with a standard case-control study, which looks at present conditions and collects retrospective self-reported data on past exposures, potentially leading to inaccuracies.