Under-reporting of outcome data may not be intentionally biased, but failure to report outcomes fully can undermine confidence in the reported findings and leaves study authors open to accusations of deliberate concealment.
To investigate the nature and potential implications of under-reporting of morbidity information in administrative hospital data.
Systematic over- or under-reporting of quantitative MWS data differed, for most variables, across the distribution of NSHD values (Table 4; P ≤ 0.007 for one-way ANOVA).
Reasons for these dichotomous observations of decreased energy intake with rising prevalence of obesity could be under-reporting of dietary consumption data [ 23], higher energy intake compared with energy expenditure [ 24], and increasingly sedentary lifestyles [ 21– 21].
The under-reporting of comorbidities in administrative data may be due to incomplete data transposition from medical records in individual hospitals to administrative databases [ 47- 49].
To date, there has not been any study that identified patient characteristics associated with the likelihood of over- or under-reporting of comorbidities in administrative data, particularly in older populations where the prevalence of comorbidities is higher.
This indicates under-reporting of 36.1 % for self-reported data, alternately, self-reported data would need to be inflated by 56.4 % to equate to data from the national insurer.
The validity of NJR data has been questioned, with loss of data or under-reporting of revision numbers a possibility, although this should affect each group equally.
A final source of ascertainment bias in IID surveillance data is the under-reporting of cases reporting recent foreign travel.
When comparing with population data, under-reporting of cancers in relatives (false negatives) reduces risk estimates, whereas over-reporting of cancers in relatives (false positives) inflates risk estimates.
For example, we have found under-reporting of caesarean hysterectomy in hospital data, possibly because the procedure is rarely a planned procedure [ 11].
