Investigators are interested in the relationship between sleep apnea and Alzheimer's disease. In order to more thoroughly understand the relationship, these investigators decide to recruit 50 participants with Alzheimer's and 50 participants without Alzheimer's, and look at their history of sleep apnea. For this study, the variables are:a. Explanatory variable: history of sleep apnea; and outcome: Alzheimer's statusb. Explanatory variable: with sleep apnea; and outcome: without sleep apneac. Explanatory variable: Alzheimer's status; and outcome: history of sleep apnead. Explanatory variable: with Alzheimer's; and outcome: without Alzheimer's

Answer = a. Explanatory variable: history of sleep apnea; and outcome: Alzheimer's status.

Step-by-step explanation:

This is Case-Control analytical study where the cases are the 50 participants with Alzheimer's and the control are the 50 participants without Alzheimer's. This type of study requires the formulation of certain hypothesis in an attempt to investigate the possible factor (sleep apnea) of a particular health condition (Alzheimer's disease). The outcome of the studies will explain the roles of specific factors in the incidence and prevalence of a disease. This type of study investigates the hypothesis that there is a relationship between suspected causal factor (sleep apnea: which is referred to as the explanatory variable) and a disease (Alzheimer's disease: which is referred to as the outcome variable). The study group is selected on the basis of presence or absence of the 'outcome variable' which is the disease where the factors (explanatory variable) are already present or not in the case (50 participants with Alzheimer's) and its controls (50 participants without Alzheimer's)