Investigation 10: Smoking and lung capacity (assigned Tues, Dec 2; due Fri, Dec 5)

You may work with one other person on this assignment, handing in one report with both names.  Word-processed reports are preferred to hand-written ones.  Please copy/paste relevant, well-labeled computer output into a Word file as appropriate.

Forced expiratory volume (FEV), the amount of air an individual can exhale in the first second of forceful breath (in liters), was measured for a group of 654 people, along with whether or not they smoke and several other variables including age. The data are in the Minitab worksheet FEV.mtw.

a) Analyze the data to address the question of whether smokers and non-smokers tend to differ with regard to lung capacity (as measured by FEV). Include comparative boxplots and numerical summaries. Also conduct a two-sample t-test and produce a 95% confidence interval for the difference in population means (Stat> Basic statistics> 2-Sample t). Summarize your conclusion.

b) Investigate whether age is a significant predictor of lung capacity (as measured by FEV). Produce a scatterplot with regression line superimposed (Stat> Regression> Fitted line plot). Report the regression equation. Interpret the slope coefficient. Also report the appropriate test statistic and p-value for testing whether the relationship between FEV and age is significant (Stat> Regression> Regression). Summarize your conclusion.

c) Produce a scatterplot of FEV vs. age, including different symbols and separate regression lines for smokers and non-smokers (Graph> Scatterplot, With regression and groups). Comment on what this graph reveals about the relationships among these three variables (FEV, age, smoking status).

d) Conduct a multiple regression analysis, predicting FEV from both age and smoking status (Stat> Regression> Regression). Report the regression equation and the value of R². Interpret both coefficients. Report the test statistics and p-values for the two regression coefficients. Summarize your conclusion.