Researchers are conducting a retrospective cohort study to examine whether use of aspirin leads to increased risk of colorectal cancer (CRC)

Researchers are conducting a retrospective cohort study to examine whether use of aspirin leads to increased risk of colorectal cancer (CRC) and will use medical records from 1990 through 2015 from a large hospital system. Selection of participants for the study should be based on which of the following: 

Patients’ CRC status (i.e. outcome status)

Patients having received care in the hospital system during the study period  

Both of the above 

Neither of the above 

In the study of aspirin and CRC from question above, some participants stopped coming for care during the follow-up period so their outcomes cannot be ascertained (i.e. they were lost to follow-up). The researchers observe that a higher proportion of participants who did not use aspirin were lost from the study compared to those did use aspirin, and they are concerned that those LTF were less likely to have developed CRC. How could this scenario bias the results of the study?    

The observed RR will not be biased 

The observed RR will be biased away from the null compared to the truth 

The observed RR will be biased towards the null compared to the truth 

None of the above