In all cases, the data are random samples from the freely-available NHANES dataset, and the variables used are;

• BPXSAR: systolic blood pressure (mmHg)
• BPXDAR: diastolic blood pressure (mmHg)
• BPXDI1, BPXDI2: two diastolic blood pressure readings
• race_ethc: race/ethnicity, coded as Hispanic, White non-Hispanic, Black non-Hispanic and Other
• DR1TFOLA: folate intake ($$\mu$$g/day)
• RIAGENDR: sex, coded as Male/Female
• BMXBMI: body mass index (kg/m$$^2$$)
• RIDAGEY: age (years)

The data are available as comma-separated files; (missing values are denoted “.”)

Note: for simplicity, all statistical analyses depicted in the graphs assume that the data represent a simple random sample (i.e. independent observations) from a population of interest. Regression analyses make the standard assumptions that the mean model is correctly specified, and (for linear regression) that the variance of outcomes is constant with respect to covariates.