A researcher wants to determine if diet has any effect on blood pressure. People were randomly assigned to receive one of the four diets: a low - fat diet, a high - fish diet, a combination of low - fat diet and high - fish diet, and a regular diet. After 6 months, blood pressures of the four diet groups were compared.
a) Name the experimental design applied in this study.
b) Identify the experimental units in this study.
c) What is the explanatory variable in this study? How many treatments does it have?
d) What is the response variable in this study?