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.