Question

The following table shows the relation between the results of a liver scan test and the correct pathology diagnosis based on necropsy, biopsy, or surgical inspection.

	Pathology
Liver scan	Abnormal (+)	Normal(-)	Total
Abnormal (+)	231	32	263
Normal (-)	27	54	83
Total	258	86	344

Q1. Calculate and interpret the sensitivity and specificity of a liver scan test based on this study.

Q2. Calculate and interpret the positive predict value (PPV) and negative predict value (NPV) of a liver test based on this study.

Q3. Calculate and interpret the false positive and false negative rates of a liver scan test based on the study.

Answer 1

Q1)

sensitively =a/a+b

=231/258

=89.53%

89% the  result will be  Positive when disease is present

sensitivity=d /(c+d)

= 54/86

=62.79%

62.79%the result will be negative when diseas is not present.

Q2)PPV=a/(a+c)

= 231/263

= 87.83%

87.83 %Disease is present when test is positive

NPV = d/(b+d)

=54/81

=66.67

66.67%disease is absent when test is negative

Q3)False positive rate=c/(a+c)

=32/263

=22.16%

false negative rate= b/(b+d)

=27/81

=0.33