If the population is believed to have a skewed distribution for one or more of its distinguishing factors (e.g., income or product usage), the researcher identifies subpopulations in the sample frame called strata. A simple random sample is then taken of each stratum. Which probability sampling method does this describe?
a. Cluster sampling
b. Stratified sampling
c. Systematic sampling
d. Simple random sampling
e. None of the above
Answer: b. Stratified sampling