Statistics
Since over 60% of patients who underwent D-dimer testing had no imaging
for PE, “Cramer’s V” method was employed. It is used to calculate
correlation coefficient (CC) for categorical variables in a 2x3 matrix,
as Phi Coeffient is applicable only for a 2x2 table. Using this
statistical method meant that correlation – the degree one variable
matched another – rather than sensitivity and specificity was the main
consideration. Interpretation was the same as for Phi correlation
coefficient; it varies between 0 and 1 without negative values,
0.05-0.09 would be considered weak correlation, 0.1-0.14 would signify
moderate correlation, 0.15-0.24 would be considered in the strong range
and 0.25 (or above) would be regarded very strong
correlation15.