Sample selection bias vs. look ahead bias

CFA Level I
#1

I’m getting confused between these two. Can someone describe the difference with examples if possible? Thanks.

#2

Sample selection bias occurs when the sample selected does not represent the overall population (does not not have the same characteristics as the population). Look ahead bias occurs when test is conducted using data that was not available at the time of the test (ex predicitng earnings for the year whereas fourth quarter earnings are not yet available.)

#3

Sample selection bias occurs when the sample selected does not represent the overall population. Look ahead bias occurs when test is conducted using data that was not available at the time of the test (ex predicting earnings for the year whereas fourth quarter earnings are not yet available.) Hope this helps.