Development of an ICD Coding Definition for Inflammatory Bowel ...

obtained beyond that which would be expected by chance compared to the maximum
possible agreement that could be obtained , simply,
observed.agreement − chance.agreement
Κ=
1− chance.agreement
However, interpretation of κ is not always straightforward because this statistic is
affected by prevalence. For example, high levels of agreement between claims and
hospital discharge summary data may emerge with low values of κ if the prevalence of
the event of interest is low. In general, at extremes of prevalence κ tends to decrease for a
fixed sensitivity and specificity.
A wide confidence interval for κ should serve as cautionary note to the reader and is often
associated with disparate values of positive and negative e agreement proportions.
4.7.4 Predictive values
The probabilities of IBD and non-IBD patients on the administrative definition having or
not having IBD were referred to as PPV or NPV, respectively. They were estimated as:
True Positive True Negative
PPV = NPV =
True Positive + False Positive True negative + False Negative
4.8 Chart reviews
As a complementary component for the study, we performed a comprehensive inpatient
and outpatient chart review on selected individuals within the time period of 1995-2006.
As each patient could have been admitted or seen in an outpatient clinic of different
Calgary Health Region hospitals, all the charts within different Calgary Health Region
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