Three categories of disorders stood out with approximately equal prevalences: depressive disorders (40.6%), anxiety disorders (38.5%) including post-traumatic stress disorder (18.4%) and alcohol/substance abuse (40.2%).
Logistic analysis has been a popular analysis tool for cross-sectional studies because 1) standard statistical software packages perform logistic analysis; 2) if the disease or outcome is rare, then odds ratios are approximately equal to prevalence ratios; and 3) if the disease is not rare, then there have not been any good alternatives.
The genetic SD for bTB susceptibility, estimated using the linear animal model, was lowest for the extreme bTB prevalence categories, with the genetic SD of very low (<0.25 prevalence) and very high (>0.75 prevalence) prevalence categories being approximately equal to half that of the low (0.25 to 0.5 prevalence) and high (0.5 to 0.75 prevalence) prevalence categories (Table 3).
The formula used is as follows: RR = OR (1 - P 0 ) + (P 0 × OR ) where RR is relative risk, OR is odds ratio, and Po is prevalence of disease in the unexposed population (assumed to be approximately equal to general population prevalence).
For example, Crohn's disease has a population prevalence approximately equal to that of congenital heart disease.
Prevalence of disease in the unexposed population (Po) required for conversion of OR to RR is assumed to be approximately equal to general population prevalence.
That is, prevalence was approximately equal at the markets (Table 2).
If the prevalence is approximately equal for each class, however, then a high overall accuracy will be highly correlated with high negative and positive predictive values and AUC, so the guidelines here are likely to carry over to these other metrics.
At low prevalence levels it can be assumed that RR, OR and HR are approximately equal.
For the purposes of analysis with sufficient power to detect small area differences in the prevalence of morbidity, the study area was divided into four contiguous sectors with approximately equal numbers of individuals in each sector.
