Ascertainment of CKD, as a silent disease, and, to a certain extent, ascertainment of acute community-acquired infections are dependent on high levels of monitoring and good access to healthcare, so we restricted our search to high-income countries.
Currently, new Y-SNPs are mainly found by sequencing a small portion of the Y chromosome for a limited number of individuals of a certain haplogroup, introducing ascertainment bias [ 13, 21, 22].
Nonetheless, the potential for misdiagnosis, under-ascertainment or over-ascertainment of certain conditions remains.
Whilst this may be partly due to more complete ascertainment of certain conditions, there are other contributory factors that could account for this discrepancy.
In that regard, one possible caveat is that, under certain conditions on mutation, the ascertainment bias of SNP genotyping arrays could lead SNPs subject to stronger biased gene conversion to be enriched, and thus lead us to slightly over-estimate the strength of biased gene conversion across the genome.
The outcome of each pregnancy diagnosed antenatally is followed-up, but ascertainment has been slow for certain laboratories in recent years.
Moreover, the accuracy of the exon length estimation for any species will increase if more data are available and if the ascertainment bias (e.g. resulting from overrepresentation of certain gene families in the sample, or from inclusion of only partially sequenced genes) is kept at the minimum.
The very neutral screening questions are expected to have led to better ascertainment, and therefore higher headache prevalence estimates, than questions requiring a certain degree or frequency or severity [26].
There is a possibility of ascertainment bias, even though we found that overall agreement was good for certain clinical signs used in the MSD case definition (sunken eyes and wrinkled skin), 6 because there was marked variation among the sites, with both over- and underdiagnosis by caretakers compared with clinicians.
It is possible that there was a degree of under-ascertainment of death in our study; however, every individual contributed a certain amount of survival time before they either died or were censored and patients were followed up annually.
