A research group is interested in the association between vitamin E supplementation and a decreased risk for osteoporosis in a group of elderly women. The team randomly samples a group of women after a strict set of inclusion criteria have been met. Then, they match each woman receiving the supplementation with two women receiving a placebo based on BMI, education, and socio- economic status. The data compiled after 10 years of follow up were analyzed using conditional logistic regression. Which of the following methods to reduce confounding was not employed in the above scenario?

a. Stratification
b. Restriction
c. Regression
d. Matching

Explanation: Social stratification relates to the division of its population into classes by the society based on sociology-economic factors such as wealth, employment, ethnicity, schooling, profession, and social standing, or related (social and political) strength.

In complex country-based, phallocentric, or feudal societies, the categorization of citizens by social strata exists most obviously, the latter centered on sociology-economic relations between classes of nobles and classes of the peasant.