A second explanation for our lower estimates of screening participation could be differences in the denominator population.
This numerical difference in the denominators is the major limitation for the MED score strategy, especially for data above the average.
The reported incidence for medical undergraduates in Sri Lanka is very high compared to these other studies [ 23- 25] even when the difference in the denominator is taken into account.
In contrast, both the Cooper and Singh methods increased the number of cancers classed as PCCRC to 7321 but, due to the differences in how the denominator was derived for each method, the PCCRC rates were 7.7%and7.5%5% respectively.
In 2005, a similar number of HbA1c tests were performed for individuals with diabetes (483,746) and without diabetes (496,616) despite large differences in the two groups' denominators.
Given potential over-estimation of the number of procedures in the 2 national surveys, possible under-estimation of the number of procedures in the VA, and differences in the types of denominators, it is possible that age adjusted rates of procedure use were too high for the national surveys and too low for the VA.
Smoothing methods need to consider and adjust for differences in the population size (denominator) for different geographic units.
We studied how papers reviewed the literature on overdiagnosis, and found 7 papers pointing out that differences in the percentages of overdiagnosis were mostly due to differences in which denominators were used in the calculations.
We suspect that most studies, without constructing a confidence interval for the RV estimate, over-interpreted the observed differences in the RVs with small denominator F-statistics, ignoring the possibility of falsely rejecting the null hypothesis of no difference when only chance was in operation.
Some respondents did not respond to all the questions, which explains the differences in denominators in some results.
