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A cutoff value is a standard value used to separate quantitative data. In the medical field, this value distinguishes between positive and negative results in a test and is also called the “pathological identification value.”
In vol.66, we introduced the cutoff value calculated using the minimum sensitivity/specificity method. Here, we explain the cutoff value calculated using Cramer’s coefficient of association for a 2 × 2 contingency table.
Cramer’s coefficient of association is an analytical method used to understand the correlation between categorical data.
Cramer’s coefficient of association for 2 × 2 contingency tables
The 2 × 2 contingency table is shown in Table 1.
[Table 1]
Cramer’s coefficient of association can be calculated using the following formula:
In a 2 × 2 contingency table, the larger the true positives (A) and true negatives (D) and the smaller the false positives (B) and false negatives (C), the larger Cramer’s coefficient of association. The values ranged from 0 to 1.
We calculate Cramer’s coefficient of association for the BMI 26 contingency table (Table 2).
[Table 2] 2 × 2 Contingency Table for the BMI Test
The BMI test value was changed from 21 to 30, and Cramer’s coefficient of association was calculated (Table 3). At a BMI of 26, Cramer’s coefficient of association reached a maximum value of 0.762. Therefore, the optimal cutoff value was 26.
[Table 3]
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