Contingency Table Calculator: Probabilities from Counts

Clinical Decision Making Program Modeled after the Calculator in
Department of Family Medicine, OUHSC Roberto Bissoni's Xpert program.
Instructions:
Using your data, fill in the four cells in the table below (the cells in red):
(Answers appear in the table below the horizontal line.)
  Disease No disease  
       
 

a

b

a + b
Test positive

       
 

c

d

c + d
Test negative

       
 

a + c

b + c

a + b + c + d
 

After you press the Calculate button, the answers appear below. 

     

Other names:

Sensitivity

a/(a+c)

True positive rate

Specifity

d/(b+d)

True negative rate

Likelihood Ratio +

 a/(a+c)/(b/b+d)

sensitivity/(1-spec)

Likelihood Ratio -

 c/(a+c)/(d/b+d)

(1-sensit)/specificity

  False positive rate

 b/(b+d)

1-specificity

False negative rate

 c/(a+c)

1-sensitivity

Probability of disease

 (a+c)/(a+b+c+d)

Prevalence

Predictive value positive

 a/(a+b)

Bayes' Theorem *

p(pos test wrong)

 b/(a+b)

 

Predictive value negative

 d/(c+d)

 

p(neg test wrong)

 c/(c+d)

 

p(test positive)

 (a+b)/(a+b+c+d)

Will test be positive?

p(test negative)

 (c+d)/(a+b+c+d)

Complement of P(tp)

Overall accuracy

 (a+d)/(a+b+c+d)

Probability correct
Copyright Robert M. Hamm, Ph.D.
Last revised: October 29, 2002
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