Validity of random-digit-dialing in recruiting controls in a case-control study

To evaluate whether the participating controls represented the underlying population in a colorectal cancer case-control study in a geographically isolated North American population.

The characteristics of the study controls recruited through Random-digit-dialing (RDD) were compared with those in the corresponding target population estimates.

Participating controls were more likely to have higher levels of education and income and were less likely to be smokers.

Study controls recruited through RDD tend to have higher socioeconomic status, which may lead to overestimation of a number of risk factors in this study.