NO.PZ2018062016000116
问题如下：
A friend has asked you to explain the sample selection bias. Which of the following will you most likely include in your explanation?
选项：
A. occurs when a study tests a relationship using sample data that was not a available on the test date.
B. some data is systematically excluded from the analysis, usually because of the lack of availability.
C. Time period over which the data is gathered is either too short or too long
解释：
B is correct. By definition, sample selection bias is some data is systematically excluded from the analysis, usually because of the lack of availability.
请问c是哪个bias