In a(n) study, a researcher measures the diets that people create for themselves and looks at changes in rates of heart disease as determined by how good or poor the diet is.

correlational

Explanation:

Correlational study: In psychology, the term correlational study is one of the types of the research design in which an experimenter or researcher tries to understand the naturally occurring relationships of one variable with that of another variable. In other words, it seeks to understand whether two or more variables share a relationship or are related to each other or not, and if they are related to each other then in what way or sense.

In the question above, the statement signifies the "correlational study".