A _____________________ sample is obtained by selecting convenient population units

A. Random

B. Quota

C. Stratified

D. Convenience

Take the formula Z = (X - )/, where is the mean of the population, X is the value of the element, Z is the z-score and is the standard deviation. What does this formula calculate?

A. Confidence interval.

B. Standard score.

C. Standard error of the mean.

D. Variance.