Relationships research questions are the final category of research questions. These are questions that concern prediction, i.e., can we predict variable X from variable Y? A relationships question would be: Is the relationship between diet and heart disease strong enough that we can predict the onset of heart disease from a knowledge of diet? This type of research question leads to correlation/regression designs. Correlation/regression designs are ex post facto designs because while we may define IVs we do not manipulate them. We do not manipulate the IV because we gather all the data at one time, hence there is no time to manipulate the IV. These designs are similar to observational studies except that we hypothesize a correlation between variables, rather than simple descriptions.