Question

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



A) What is the expected CD4 count for a patient taking supplements who has had HIV for 2.5 years? (5 points)

                       Y=

B) What is the expected CD4 count for a patient not taking supplements who was diagnosed with HIV at study enrollment? (5 points)

                        Y =

C) What is the expected CD4 count for a patient not taking supplements who has had HIV for 2.5 years. (5 points)

                          Y=

Answer 1

Sol:

Y = 302 + 15.1 Supplements – 18.6 Duration of HIV

A) What is the expected CD4 count for a patient taking supplements who has had HIV for 2.5 years? (5 points)

                       Y= 302 + 15.1*(1) – 18.6*(2.5) = 363.6

B) What is the expected CD4 count for a patient not taking supplements who was diagnosed with HIV at study enrollment? (5 points)

                        Y = 302 + 15.1*0 – 18.6*0 = 302

C) What is the expected CD4 count for a patient not taking supplements who has had HIV for 2.5 years. (5 points)

                          Y= 302 + 15.1*0 – 18.6*2.5 = 348.5