[R] correlation and causality examples

[Albyn Jones]

On Sat, Nov 15, 2003 at 03:49:29PM +0100, Jean lobry wrote:
> Dear All,
> 
> I'am looking for examples showing that correlation does not imply
> causality, the targeted audience consists of undergraduate students
> (their first year at the university but in the BioMathStat track).
> All practicals are under R.
> 

The dataset below contains data by state, including population in 
thousands, area in square miles, percent urban population, percent 
below poverty line, whether there are gun registration laws or not, 
and the number of homicides. The socioeconomic data are from 1990/91,
from the census bureau as I recall.
 
The gun registration indicator is taken from a USA Today article 
(Tuesday, January 7, 1992, PAGE 5A).  The article reported that
gun registration laws lead to increased numbers of murders 
(homicides), a conclusion reached by comparing the mean number of 
homicides in states with gun registration laws to states without 
registration laws.  

"Guns" <- 
structure(.Data = list(
"pop" = c(4089, 2372, 30380, 3291, 598, 13277, 1135, 2795, 11543, 5996, 
   4860, 9368, 4432, 5158, 6737, 635, 7760, 18058, 10939, 11961, 1004,
   3560, 4953, 17349, 1770, 5018, 570, 3750, 3377, 680, 6623,
   1039, 5610, 2495, 3713, 4252, 1235, 2592, 808, 1593, 1105,
   1548, 1284, 3175, 2922, 703, 6286, 567, 4955, 1801, 460.), 
"area" = c(52.4, 53.2, 163.7, 5.5, 0.1, 65.8, 10.9, 56.3, 57.9, 10.6, 
   12.4, 96.8, 86.9, 69.7, 53.8, 70.7, 8.7, 54.5, 44.8, 46.1, 1.5, 32, 
   42.1, 268.6, 84.9, 71.3, 656.4, 114, 104.1, 2.5, 59.4, 83.6, 36.4, 
   82.3, 40.4, 51.8, 35.4, 48.4, 147, 77.4, 9.4, 121.6, 110.6, 69.9, 
   98.4, 77.1, 42.8, 9.6, 65.5, 24.2, 97.8), 
"urban" = c(60, 54, 93, 79, 100, 85, 89, 61, 85, 84, 81, 70, 71, 53, 
   50, 53, 89, 84, 74, 69, 86, 55, 61, 80, 87, 76, 68, 88, 82,
   73, 63, 57, 65, 69, 52, 68, 45, 47, 53, 66, 51, 73, 88,
   68, 71, 50, 69, 32, 66, 36, 65.), 
"poverty" = c(19, 18.4, 14.2, 5.8, 19.2, 14.1, 10, 10.1, 13.3, 10.2, 
   9.3, 13.9, 12, 13.6, 13.2, 13.5, 9, 14.1, 11.8, 10.8, 8.2, 16.5, 
   16.9, 16.8, 9.8, 26.2, 11.2, 14.2, 12.1, 8.1, 16, 13.7, 14.1, 11.1, 
   17.4, 22, 12.5, 23.8, 15.8, 10.9, 7.1, 20.9, 10.7, 15.8, 11.3, 13.5, 
   10.6, 7.1, 9.2, 17.2, 10.6), 
"gunreg" = c(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
   1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.), 
"homicides" = c(410, 240, 3710, 170, 489, 1300, 44, 62, 1270, 200, 540, 
   1020, 100, 550, 730, 11, 350, 2550, 760, 740, 38, 350, 470, 2660,
   43, 220, 56, 290, 155, 32, 720, 21, 380, 150, 260, 760,
   23, 370, 29, 43, 32, 160, 135, 220, 120, 9, 550, 24, 240,
   135, 20.)), 
names = c("pop", "area", "urban", "poverty", "gunreg", "homicides"), 
row.names = c("AL", "AR", "CA", "CT", "DC", "FL", "HI", "IA", "IL", "MA", 
   "MD", "MI", "MN", "MO", "NC", "ND", "NJ", "NY", "OH", "PA", "RI", "SC", 
   "TN", "TX", "UT", "WA", "AK", "AZ", "CO", "DE", "GA", "ID", "IN", "KS", 
   "KY", "LA", "ME", "MS", "MT", "NE", "NH", "NM", "NV", "OK", "OR", "SD", 
   "VA", "VT", "WI", "WV", "WY"), class = "data.frame")


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http://www.reed.edu/~jones    Albyn Jones	  jones at reed.edu
Reed College, Portland OR 97202             (503)-771-1112 x7418