Consider the gonorrhoea dataset containing infection rates in the US by year, age, ethnicity and gender:

 

   Year Age.Group           Ethnicity Gender Rate
1  2007    0 to 4 Non-Hispanic Whites   Male  0.3
2  2007    5 to 9 Non-Hispanic Whites   Male  0.0
3  2007  10 to 14 Non-Hispanic Whites   Male  0.2
4  2007  15 to 19 Non-Hispanic Whites   Male 31.0
5  2007  20 to 24 Non-Hispanic Whites   Male 76.9
6  2007  25 to 29 Non-Hispanic Whites   Male 63.4
7  2007  30 to 34 Non-Hispanic Whites   Male 41.0
8  2007  35 to 39 Non-Hispanic Whites   Male 31.8
9  2007  40 to 44 Non-Hispanic Whites   Male 25.4
10 2007  45 to 54 Non-Hispanic Whites   Male 13.7
...

 

Run a linear regression of the response variable Rate on all the other variables as main effects. Restrict the analysis to the 15-to34-year olds. Store your result in an object called gonorrhoea_lm.

(from: Cotton, 2013, Learning R, O’Reilly)