A researcher wanted to know whether consumption of green tea on a daily basis reduces LDL (bad) cholesterol. She obtains a random sample of 500 subjects. Each subject consumes at least 1 cup of green tea daily for 1 year. After 1 year, the researcher determines whether the subjects LDL cholesterol decreased, or not.

Indicate whether a confidence interval for a proportion or mean should be constructed to estimate the variable of interest. Justify your response.