A study was conducted in a nursing home to examine the association of hand-washing and Gastroenteritis. Residents with the disease were recruited and others from the nursing home without the disease were subsequently selected. This kind of study is known as:

The correct answer is case control study.

Explanation:

A study in which a comparison is made between the patients carrying the disease with the patients not carrying the disease is known as the case-control study. In the mentioned study, the one carrying the disease is termed as cases, and the one that does not possess the disease is termed as controls.  

This form of study is generally done to predict the association between the disease and the risk factor. In case-control studies, only observation is done as no attempt is made to change the course of the condition. The prime objective of the study is to predict the exposure of the risk elements for the individuals present in two groups, that is, controls and cases. This form of study is also called case-referent studies or retrospective studies.  

the answer is sex-linked recessive.