a study is conducted in patients with HIV A study is conducted in patients with

Question

a study is conducted in patients with HIV A study is conducted in patients with HIV. The primary outcome is CD4 cell count which is a measure of the stage of the disease. Lower CD4 counts are associated with more advanced disease The investigators are interested in the association between vitamin and mineral supplements and CD4 count A multiple regression analysis is performed relating CD4 count to use of supplements (coded as 1=yes, 0=no) and to duration of HIV, in years (i e., the number of years between the diagnosis of HIV and the study date) For the analysis, Y=CD4 count. Y = 302 + 15 1 Supplements - 18.6 Duration of HIV What is the expected CD4 count for a patient taking supplements who has had HIV for 2.5 years? Y = What is the expected CD4 count for a patient not taking supplements who was diagnosed with HIV at study enrollment? Y = What is the expected CD4 count for a patient not taking supplements who has had HIV for 2.5 years Y =

Explanation / Answer

Solution:

We have multiple regression equation

= 302 + 15.1 (Supplements) – 18.6 (Duration of HIV)

Now

(a) The expected CD4 counts for a patient taking supplements who has had HIV for 2.5 years

So supplements=1 (As patient takes supplement yes=1)

Duration of HIV= 2.5

Hence expected CD4 count is:

= 302 + 15.1 (1) – 18.6 (2.5) = 270.6

(b) The expected CD4 counts for a patient not taking supplements who has had HIV at study enrolment.

Value of supplement = 0 (As patient is not taking supplement)

Duration of HIV=0 (the no. of years between the diagnosis of HIV and study date, here it was diagnosed with HIV at study time, hence the no. of years is zero)

Hence

The expected CD4 counts for a patient not taking supplements who has had HIV at study enrolment.

= 302 + 15.1 (0) – 18.6 (0) = 302

(c)

The expected CD4 counts for a patient not taking supplements who has had HIV for 2.5 years

= 302 + 15.1 (0) – 18.6 (2.5) = 255.5

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