Type of biases
Bias, which affects validity, exists in all types of research designs.
1. Selection Bias : A distortion in true study finding due to improper selection procedures or it is due to an effect of selection process
Such as; case selection, sample bias, loss-to-follow up bias, disease spectrum bias, participation bias, study examination bias, image-based selection bias ,ect.
* Most common type of bias.
1.1 Prevalence-incidence bias: most common type of case-control study, but not often a problem in cohort studies and experiments
1.2 Admission rate (Berkson’s) bias: due to selective factors of admission to hospitals, and occurs in hospital-based studies
- More common in observational studies, in particular case-control studies
1.3 Non-response bias: due to refusals to participate in a study
- More serious in observational studies. In particular, sample surveys are more prone to this type of bias.
Some potential sources of selection biases:
1. Self selection bias
2. Selection of control group