Subject Code : PHCM9498
Assignment Task

 

Question 1

A cross-sectional study was undertaken in the United States to determine if there is an association between blood lead level (measured in micrograms per decilitre: μg/dL) and diastolic blood pressure (measured in millimetres of mercury: mmHg). It is hypothesised that as blood lead level increases, diastolic blood pressure increases.
 

The following data were recorded for each of 431 participants:

id: unique subject identifier
dbp: diastolic blood pressure (mmHg)
lead: blood lead level (μg/dL)
age: age (years)
sex: sex (1 = male, 2 = female)
race: race (1= white, 2 = black, 3 = other)
smoke: current smoker (1 = no, 2 = yes)
bmi: body mass index (kg/m2)
potassium: serum potassium (mmol/L)
sodium: serum sodium (mmol/L)
anti: currently taking medication for high blood pressure (0 = no, 1 = yes)
 

The dataset lead.dta is posted on the Moodle site (Assessments > A3: Assignment 2).
 

(a) Based on the research question presented above, which is the outcome and which is the explanatory variable?
 

(b) Using Stata, generate a scatterplot to represent the association between blood lead level and diastolic blood pressure. Comment on the important features of the scatterplot.
 

(c) Estimate, and interpret, the correlation coefficient between blood lead level and diastolic blood pressure.
 

(d) Fit a simple linear regression model regression diastolic blood pressure on blood lead level. Provide a screenshot of the output including the Stata command. Interpret the regression coefficients from the output you have reported.
 

(e) What is the R2 value? Interpret it.
 

(f) What is the predicted diastolic blood pressure for a person with a blood lead level of 2.5 micrograms per decilitre? Show your working. 
 

(g) Are the assumptions of Normality met for this linear regression model? Provide supporting statistics and graphs to justify your answer.

 

 

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  • Posted on : April 14th, 2019
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