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st: mkspline question


From   Vivien Lee <viviensl@email.arizona.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: mkspline question
Date   Wed, 6 Mar 2013 15:16:33 -0700

Hello,

I have a few questions regarding splines and creation of linear regression
with a spline at a specified knot.  Some background:

I am plotting injury count (var: cinj) over a number of years (var:year)
(1999-2010).  Associated with cinj and year is a mine id number (var:
mineid).  Currently, my dataset lists the number of injuries per year per
mine id number.  I am interested in comparing "company C" (var: compc == 1)
owned mines against all other mining companies (var: compc == 0).  I'd like
for both series to show up on the same graph (company C owned mines vs. all
other mines, averaged injury count each year).  I'd also like to show the
95% confidence interval (bar and spike) of the average number of injuries
per year.  The spline should occur in year 2004 as a new risk management
system was introduced at the time.  I want to show that there is a
difference in slope of average injury count per year before 2004 and after
2004 for company C owned mines versus mines not owned by company C
(basically to show whether the new risk management system worked or not).

I had tried to perform an lfit plot of my data but the slopes were not
meeting in 2004.  It was suggested that I look at using a spline command to
depict the data instead.  I'm unsure as to how to set up the command for
this.  Thanks you very much for your time and help.

Regards,
Vivien
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