There was over 95% agreement between chart abstractors on the sample of charts selected for validation.
However, in practice many data sets are samples from the population, for example, data abstracted from a sample of charts, data from surveys [ 40, 41], and public use microdata files such as census sample files [ 42- 46].
However, in a study by Quan et al assessing a random sample of charts, obesity had prevalence 2.7% in ICD-9-CM DAD and 1.9% in ICD-10 DAD [ 10] similar to the rate seen in this population.
Although we extracted information on only a small sample of charts on our patients, which is insufficient to interpret our results, other studies have reported that the number of medical diagnoses or medications have not been shown to be predictive of outcome in the GDH setting [ 26].
The sampling frame of charts was derived from the BCPDR and included all admission episodes with discharge dates between April 1, 2010 and March 31 , 2012
A random sample of chart numbers (40% of the total number of charts present) was then drawn and the corresponding women were approached to assess eligibility and interest in participating in the study.
We audited a random sample of 50 charts of patients from 310 eligible charts.
This was a retrospective cohort study based on expert chart review of a random sample of 1200 charts of clients discharged in fiscal year 2009 2010 from publicly funded HC programmes in Manitoba, Quebec and Nova Scotia, Canada.
Phase 1 was a retrospective chart audit of a systematic random sample of patient charts, and phase 2 included a structured interview of a prospective random sample of emergency and intensive care unit nurses and physicians.
Participants' charts were audited by a senior GP (CPB) and a random sample of twenty charts (31%) was re-audited by CPB to evaluate intra-rater reliability.
Although this study represents a convenience sample because of chart availability and may represent reporting bias, the case-patients reported had high case-fatality and disability rates at last known follow-up evaluation at 60 days.
