Study design and population

This retrospective cohort study considered all PLHIV who were registered in Sungai Buloh Hospital, Selangor, Malaysia, between January 1, 2007 and December 31, 2016. This tertiary hospital is one of the centers of excellence for infectious disease in Malaysia.

Only ART-naive patients aged >15 years were included, while those discharged from the hospital without ART were excluded. The sample size was determined through the survival formula in the PS: Power and Sample Size Calculations software.[7] The significance level was 0.05, and the power was 80%. Considering that an estimated 10% of the sample might have 30% or more variables with incomplete data, an additional 10% of subjects would be sampled to achieve the final required sample size. Thus, based on the calculations, a total of 374 subjects were required for this study. Patients' data were assessed from the inclusion cutoff period up to 31 August 2018.

A large sample was available, but there were time constraints to process this data, thus systematic sampling method was adopted. The sampling interval (k) was 16 (calculated by dividing the total eligible patients with the required sample size). To initiate the first selection, “7” was randomly generated in Microsoft Excel using the formula: =RANDBETWEEN (1, 16). Accordingly, from the patients' list, which was sorted according to the date of ART initiation, patient number 7 was selected as the first subject, and every subsequent 16^thpatient was included (i.e., 7^th, 23^rd, 39^thpatient, and so on).