Why Do Labor Economists Often Find It Difficult to Estimate

Multiple Choice

Why do labor economists often find it difficult to estimate the ceteris paribus return to education, in terms of wage, using non-experimental data?

A) Education level in non-experimental data is probably dependent on other omitted factors that also affect wage.
B) In a non-experimental setting, education level is often difficult to measure.
C) Wage is often reported unreliably and inaccurately.
D) Experience, another factor that also affects wage, is generally difficult to measure.