By having accuracy and sensitivity, can we calculate specificity? How about calculating sensitivity from accuracy and specificity?

My second question is, if sensitivity and specificity both increase 1% how much does accuracy change (1% or more)?


Regarding your first question: only if you know how many positive and negative samples you have. Look at three special cases:

  1. You have the same amount of positive and negative samples. Then accuracy is the mean of sensitivity and specificity.
  2. All samples are positive. Accuracy and sensitivity are the same.
  3. All samples are negative. Accuracy and specificity are the same.

In general, accuracy is a weighted sum of sensitivity and specificity with the weights being the proportion of positive and negative samples respectively.

Second question: It is always exactly 1%. This is because the weighted sum of two identical numbers does not depend on the weights, as long as they add up to 1.


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