The downward trend in smoking you saw in the last exercise is good news for the health of babies, but will it ever stop?
a) Explain why you can't use the linear model you created in Exercise 22 to see when smoking during pregnancy will cease altogether.
b) Create a model that could estimate the year in which the level of smoking would be 0%.
c) Comment on the reliability of such a prediction.
Exercise :
Smoking and pregnancy 2003. The organization Kids Count monitors issues related to children. The table shows a 50-state average of the percent of expectant mothers who smoked cigarettes during their pregnancies.
|
Year
|
% Smoking While Pregnant
|
Year
|
% Smoking while Pregnant
|
|
1990
|
19.2
|
1997
|
14.9
|
|
1991
|
18.7
|
1998
|
14.8
|
|
1992
|
17.9
|
1999
|
14.1
|
|
1993
|
16.8
|
2000
|
14.0
|
|
1994
|
16.0
|
2001
|
13.8
|
|
1995
|
15.4
|
2002
|
13.3
|
|
1996
|
15.3
|
2003
|
12.7
|
a) Create a scatterplot and describe the trend you see.
b) Find the correlation.
c) How is the value of the correlation affected by the fact that the data are averages rather than percentages for each of the 50 states?
d) Write a linear model and interpret the slope in this context.