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True negatives (TN)

True Negatives (TN) = patients who do NOT have the disease AND the test is negative. In SPSS Crosstabs: Disease=No row, Test=Negative column. Example: out of 100 healthy patients, 80 tested negative → TN = 80.

False positives (FP)

False Positives (FP) = patients who do NOT have the disease BUT the test was positive (false alarm). In SPSS Crosstabs: Disease=No row, Test=Positive column. Example: 20 healthy patients tested positive → FP = 20. Specificity = TN ÷ (TN + FP) = 80 ÷ 100 = 80%.

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