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Re: st: using roctab when lower values of 'classvar' indicate higherrisk
Morrison Hodges wrote:
The manual says that when using 'roctab', higher values of 'classvar' must
It is only by *convention* that, in ROC methods, larger values of the test
result are more indicative of disease (or, in this case, death). You can
legitimately satisfy this convention in this situation by redefining your test
result as Y = -EF.
indicate higher risk. I have data using a cardiac variable called ejection
fraction (EF) as 'classvar', which varies from 0.00 to 1.00, with lower
values indicating higher risk. The 'refvar' is 'status', with 0=alive and
1=dead. The lower the EF the more likely the patient is dead.
roctab status ef, graph
produces a curve below the 45 degree line; I want the curve to be above the
45 degree line. What is a legitimate way to make the curve be above the 45
degree line? Exchange 'refvar' values? Subtract 'classvar' values from 1?
Something else? Thanks.
Alternatively exchanging the <refvar> values will give you a different and
likely unwanted result: a plot of specificity vs. 1-sensitivity in the situation
where it is believed that lower test values are more indicative of disease or
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