To demonstrate the effect of multicollinearity between predictors in regression models in real life epidemiologic studies, in this section we present the analyses of empirical data from Cameron County Hispanic Cohort (CCHC) using linear regression models. The study population is the Brownsville population represented by CCHC initiated in Cameron County, Texas in 2004, and currently includes more than 3000 participants of age 18 years or older. Information regarding sampling and eligibility criteria of the cohort participants and data collection has been reported previously [29 (link)].
The response variables of interest were baseline systolic blood pressure and diastolic blood pressure as continuous variables. Readings of blood pressure were taken following standard protocols. Participants sat quietly for 5 minutes and then readings were taken three times 5 minutes apart using a Hawksley Random Zero sphygmomanometer. Diastolic blood pressure was determined at the 5th Korotkoff sound. The final pressure was based on the average of the 2nd and 3rd measurements.
The predictors of interest were Body mass index (BMI) and waist circumference (WC), known to be highly correlated obesity related risk factors. Other covariates, such as age at initial visit (baseline), family history of hypertension, smoking and drinking status, as well as education were included in the regression analysis. Waist circumference (visceral adiposity) was measured at the level of the umbilicus to the nearest 10th cm, with the participant in a standing position and breathing normally. Height was measured to the nearest 10th cm using a stadiometer. Weight (to the nearest 10th kilogram) was measured on a calibrated beam balance. BMI was calculated as weight in kilograms divided by height squared in meters (kg/m2).
The Committee for the Protection of Human Subjects at the University of Texas Health Science Center at Houston approved the study protocol, written consent forms and procedures and free and informed consent was obtained from all subjects. The investigators had no conflict of interest to disclose at consent.
The response variables of interest were baseline systolic blood pressure and diastolic blood pressure as continuous variables. Readings of blood pressure were taken following standard protocols. Participants sat quietly for 5 minutes and then readings were taken three times 5 minutes apart using a Hawksley Random Zero sphygmomanometer. Diastolic blood pressure was determined at the 5th Korotkoff sound. The final pressure was based on the average of the 2nd and 3rd measurements.
The predictors of interest were Body mass index (BMI) and waist circumference (WC), known to be highly correlated obesity related risk factors. Other covariates, such as age at initial visit (baseline), family history of hypertension, smoking and drinking status, as well as education were included in the regression analysis. Waist circumference (visceral adiposity) was measured at the level of the umbilicus to the nearest 10th cm, with the participant in a standing position and breathing normally. Height was measured to the nearest 10th cm using a stadiometer. Weight (to the nearest 10th kilogram) was measured on a calibrated beam balance. BMI was calculated as weight in kilograms divided by height squared in meters (kg/m2).
The Committee for the Protection of Human Subjects at the University of Texas Health Science Center at Houston approved the study protocol, written consent forms and procedures and free and informed consent was obtained from all subjects. The investigators had no conflict of interest to disclose at consent.
