Table 2.
Possible Bias with Controls and Preventive Measures
| Type of control | Type of bias | Measures to prevent bias |
|---|---|---|
| Different treatment control | Channeling bias1: Patient comorbidities and prognostic factors compel the investigator to decide which treatment arm they will be placed, a more aggressive one versus one with fewer risks. | Randomization |
| No treatment control | Misclassification bias2: Improper assignment of the exposure or disease status. The bias may overestimate or underestimate the treatment effect. | Clear definitions, blinding, standard procedures, good measuring methods |
| Hospital controls | Do not represent the source populations from which cases arise. | Use population based controls, controls with disease not related to exposure. Select only for hospital cases |
| Friend/Spouse/Sibling control | Selection bias3: Due to overlapping nature of these controls. The bias may overestimate or underestimate the treatment effect. | Same selection criteria for cases and controls, high rate of follow-up and high response rate |
| Historic control | Chronology bias1: Due to differences in time and place of controls and treatment groups. Bias also possible due to differences in diagnostics, treatments and outcome assessment methods between the two comparative groups. The bias overestimates the treatment effect. | Use historic controls from very recent past or conduct a prospective cohort study or a randomized controlled trial |
1
Pannucci CJ, Wilkins EG. Identifying and Avoiding Bias in Research. Plastic and Reconstructive Surgery. 2010;126(2):619–625
2
Jennings JM, Sibinga E. Research and statistics: understanding and identifying bias in research studies. Pediatr Rev. Apr 2010;31(4):161–162
3
Austin H, Flanders WD, Rothman KJ. Bias arising in case-control studies from selection of controls from overlapping groups. Int J Epidemiol. Sep 1989;18(3):713–716