Modeling time-to-good control of hypertension using Cox proportional hazard and frailty models at Bahir-Dar Felege Hiwot Referral Hospital

Abstract

Purpose:

The main purpose of this study was to explore possible modeling approaches of time-to-good control of hypertension using Cox proportional hazard (Cox-PH) and frailty models, using data from Bahir-Dar Felege Hiwot Referral Hospital.

Patients and methods:

An institution-based retrospective cohort study was conducted in June 2014. The study population consisted of all hypertensive patients who had visited the hospital at least three times between January 1, 2009, to December 31, 2013. Five hundred patients were selected using simple random sampling. The data were collected by trained data collectors using a checklist. Statistical Package for the Social Sciences version 20 and R software were used for data entry and to process the data, respectively. First, a single covariate analysis was done using Cox-PH and univariate frailty models. Then, all variables that were significant were included in the multivariable analysis.

Results:

The median survival time of hypertensive patients to attain good control was 48 months, and the mean survival time was 43.6 months. Age and systolic blood pressure (SBP) of patients had a negative relationship with the outcome. However, fasting blood sugar (FBS) had a positive relationship with the outcome. Moreover, the results showed that the progression of outcome depended on the patient’s age.

Conclusion:

Cox-PH-based analysis revealed that the factors that affected good control of hypertensive patients were age, SBP, FBS, and creatinine. The result of the univariate frailty analysis showed that there was unobserved heterogeneity between individuals in the study setup, which indicated that there were unmeasured covariates.

Keywords::

• hypertension
• time-to-event
• Cox proportional hazard
• frailty model
• Schoenfeld residuals
• good control of hypertension

Acknowledgments

We would like to say thank you very much for all staff members of Bahir-Dar Felege Hiwot Referral Hospital for their great support and commitment. Our warmest gratitude goes to the Ethiopian Ministry of Education for financial support. The authors are grateful to all health professionals and hypertensive patients who participated in the study.

Author contributions

SHH and EMS conceived and designed the study, developed data collection instruments, and supervised data collection. EMS participated in the testing and finalization of the data collection instruments and coordinated study progress. SHH and EMS performed the statistical analysis, and SHH wrote all versions of the manuscript. Both authors critically revised and approved the final manuscript.

Disclosure

The authors report no conflicts of interest in this work.