These differences could be due to a selection bias, as our patients were selected by the severity of kidney damage (which resulted in a lower frequency of focal class and a higher one in the mixed class), or to a limited reproducibility of the classification, as suggested by Ford et al. [ 20].
Due to a selection bias the influence of patent age on its value cannot be determined.
This may be due to a selection bias caused by the referral policy by the clinician for an MR examination.
Lastly, this result could also be due to a selection process of the groups, which may differ by country.
We can therefore accept H B, with the reservation that part of this improvement may be due to a selection bias (weaker students leave).
Each time we find some relation between different properties, we must understand clearly which is real (physical) and which is simply due to a selection effect.
Moreover, a part of the difference is due to a selection effect: salaried physicians prefer shorter working hours and prefer to work less intensively.
These findings confirm that spatial skills are trainable and suggest that the high spatial skills level of carpenter apprentices is due to a selection bias as well as to the training that they receive during their apprenticeship.
Comparatively, the higher rate of patient information reported by our survey participants seems encouraging but might be due to a selection bias: the majority of surgeons that volunteered to answer our questionnaire had probably a strong interest in adhesion-related issues.
This may be due to a selection bias in the national surveillance data since not all notified TB patients are tested for HIV.
This analysis suggests a reduced genetic diversity in resistant mosquitoes potentially due to a selection associated with a mutation conferring resistance.
