As available samples differed in ascertainment method (i.e., ascertained for ADHD or population based) we tested for SNP associations with IQ in an ADHD background and in a non-ADHD, general population, background.
Studies ascertaining cases of type 2 diabetes by self report involved uncertainty in ascertainment, and thus numbers of cases were revised by a positive predictive value (proportion of verified cases among self reported cases) (see supplementary information and table S3).
Moreover, given the variability in ascertainment of NSSI that can be attributed to small differences in assessment methods, agencies should set in place identification protocols that rely on standardized assessment procedures.
There also were differences in ascertainment of drug use at CCC compared with JHU.
The variability in mortality by setting may also reflect differences in ascertainment criteria, or testing and surveillance methods.
Despite the differences in ascertainment, iron deficiency was associated with an increased risk of febrile seizures in five of the eight studies [3], [4], [6], [8], [9].
Furthermore, several studies have been based on registry data, which may be hampered by variations in ascertainment of the diagnosis and reporting strategies [20].
This adjustment disregards matching and does not account for variability in ascertainment; bias could still arise if ascertainment probability is associated with the matching factors.
Data collection methods differ between the regional registries and some differences in ascertainment may exist.
Differences in ascertainment of cases are a possible reason for this effect.
No differences in ascertainment rates existed by diabetes diagnosis year (data not shown).
