Calculator for EPV
Version 1.12 Revised: 2001-12-10

You can calculate Etiologic Predictive Value (EPV) by entering:

The sensitivity of the test.
Theta, i.e. the relation between the proportion of positive tests in a healthy control population and in a population of symptomatic carriers. The value 1.0 is suggested and will be appropriate for most situations.
The number of positive and negative tests obtained in the group of symptomatic patients.
The number of positive and negative tests obtained in a healthy control population.

The numbers already filled in is an example of evaluating a throat culture used during summer season in children 3-15 years of age¹. Press "Calculate" to see EPV being calculated. Then alter the numbers to fit your situation and press "Calculate".


1.	Set the preconditions for the calculation
	Sensitivity of the test to discover the marker it is designed to detect (must be >0 and <1)
	Theta, i.e. the relation between the proportion of asymptomatic and symptomatic carriers. Theta must be >0. For more information on theta click on FAQ in the menu to the left (if you do not see a menu to the left click on "Back to Main menu" at the bottom of this page).

2.	Fill in the number of positive and negative tests among patients and the healthy comparison group
			Symptomatic patients	Healthy individuals
Positive test T+
Negative test T-

3.	Calculate Etiologic Predictive Value (EPV) by pressing the button


4.	View and interpret the result
Warning messages:
		Estimation	95% confidence interval
	Positive-EPV:
	Negative-EPV:

Useful hints

Do you get a warning message although all prerequisites for EPV are fulfilled? One possible explanation might be that you are using something else than a dot as decimal limiter. For example, the sensitivity must be written as 0.9 not as 0,9.

This calculator works off line. You can save this webpage on your computer as a file and run it without being connected to the internet. However, it is advisable to check for updated versions once or twice a year.

References

Gunnarsson, R.K., Holm, S.E. and Söderström, M. `The prevalence of beta-haemolytic streptococci in throat specimens from healthy children and adults. Implications for the clinical value of throat cultures' , Scand J Prim Health Care, 15, 149-155 (1997).

Disclaimer

The result from the EPV-Calculator has been compared with the outcome of manual calculations as well as calculations made in an Excel-file. Thus, the calculator is carefully tested and has been found to be reliable. However, we do not take legal or financial responsibility for miscalculations. The responsibility lies wholly on the user of this calculator

Ronny Gunnarsson MD PhD
Department of Primary Health Care
Göteborg University
SWEDEN

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