Suppose that a 20 item scale is developed to predict whether patients applying f

Question

Suppose that a 20 item scale is developed to predict whether patients applying for hospice care will die within 90 days from the application date. Half the items are completed by the patient's physician while the remaining items are completed by a family member or close friend. In order to study the characteristics of the new instrument, researchers administer the scale to 771 patients applying for hospice care. Of the patients who die in the succeeding 90 days, the scale correctly predicts the death of 301 but incorrectly predicts that 44 will live longer than 90 days. Of the 426 applicants who live longer than 90 days, the scale correctly predicts longevity for 398 but incorrectly predicts death for 28.

Scale Dies within 90 days Lives longer than 90 days

Predicts Death

within 90 days 301 28

Predicts will not

die within 90 days 44 398

What is the positive predictive value of this scale?

Explanation / Answer

Positive predictive value of this scale is calculated by using

              PPV value = 301 / (301+44) = 44

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