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Statistical tests Sample size calculation

Diagnostic test evaluation calculator

Instructions: enter the number of cases in the diseased group that test positive (a) and negative (b); and the number of cases in the non-diseased group that test positive (c) and negative (d).

Disease prevalence

If the sample sizes in the positive (Disease present) and the negative (Disease absent) groups do not reflect the real prevalence of the disease, you can enter the disease prevalence (expressed as a percentage) in the corresponding input box.

Next click the Test button.

Number or true positives (disease present, test positive) Number of false negatives (disease present, test negative) Number of false positives (disease absent, test positive) Number of true nagatives (disease absent, test negative)

Disease
Test	Present	n	Absent	n	Total
Positive	True Positive	a=	False Positive	c=	a + c
Negative	False Negative	b=	True Negative	d=	b + d
Total	a + b	c + d

Disease prevalence

If the ratio of cases in the Disease Present and Disease Absent groups
does not reflect the disease prevalence, enter:

disease prevalence (%):

Results

Statistic	Value	95% CI
Sensitivity
Specificity
Positive Likelihood Ratio
Negative Likelihood Ratio
Disease prevalence (*)
Positive Predictive Value (*)
Negative Predictive Value (*)
Accuracy (*)

(*) These values are dependent on disease prevalence.