# st: multicollinearity

 From Chris Witte To statalist@hsphsun2.harvard.edu Subject st: multicollinearity Date Wed, 19 Nov 2008 12:06:20 -0800 (PST)

```Is there another way to get the following module (the link isn't working for me)?

Example .  Stata learning module on regression diagnostics:  Multicollinearity
. . . . . . . . . . . . . . . . . .  UCLA Academic Technology Services
12/03   http://www.ats.ucla.edu/stat/stata/modules/reg/multico.htm

Also, I have read that -anova- and -regress- will drop variables that have collinearity problems, but I have never had Stata drop variables on me.  For example:

sysuse auto
reg price headroom trunk weight length turn displacement gear_ratio

Source |       SS       df       MS              Number of obs =      74
-------------+------------------------------           F(  7,    66) =    8.18
Model |   295089440     7  42155634.3           Prob > F      =  0.0000
Residual |   339975956    66  5151150.85           R-squared     =  0.4647
Total |   635065396    73  8699525.97           Root MSE      =  2269.6
------------------------------------------------------------------------------
price |      Coef.   Std. Err.      t    P>|t|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
headroom |  -788.1489   423.1895    -1.86   0.067    -1633.074    56.77608
trunk |   109.2235   103.9332     1.05   0.297    -98.28582    316.7328
weight |   5.300069   1.331056     3.98   0.000     2.642531    7.957607
length |  -73.59571   42.42778    -1.73   0.087    -158.3055    11.11408
turn |  -301.2525   124.9576    -2.41   0.019    -550.7384   -51.76669
displacement |    11.4282   7.622549     1.50   0.139    -3.790711    26.64711
gear_ratio |   2236.615   1051.394     2.13   0.037     137.4391    4335.791
_cons |   7795.908   6103.469     1.28   0.206    -4390.061    19981.88
------------------------------------------------------------------------------

and the correlation between weight and length is 0.9460.  Why aren't one of these variables dropped?  Does there have to be perfect correlation for dropping variables?

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```