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# Re: st: ST: Calculating first differenced correlations

 From Steven Samuels To statalist@hsphsun2.harvard.edu Subject Re: st: ST: Calculating first differenced correlations Date Tue, 7 Dec 2010 20:30:56 -0500

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Nicole White wrote: "I am trying to figure out how to calculate the correlation of first differences for two variables, poverty and violence rates, for the years 1993 to 2004. "
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You can do this by hand or by using time series commands; see the example below. I'm not expert in this area, but analyzing log crime and log poverty might be worthwhile.
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Steve

**************************CODE BEGINS**************************
clear
set obs 12
gen year = _n + 1992
list
set seed 4568
gen crime = uniform()*2500
gen poverty = crime[_n-1] +uniform()

// First by hand
gen d1crime= crime-crime[_n-1]
gen d1pov = poverty-poverty[_n-1]
corr d1pov d1crime

// With Time series operators d. (= d1.)
tsset year

list d1pov d.poverty d1crime d.crime d1.crime
corr d.poverty d.crime
scatter d.poverty d.crime
***************************CODE ENDS***************************

On Dec 7, 2010, at 5:59 PM, White, Nicole (UMSL-Student) wrote:

Hello--
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I am trying to figure out how to calculate the correlation of first differences for two variables, poverty and violence rates, for the years 1993 to 2004. I assume that I need to identify my dataset as a time series, so I entered the tsset command and identified the time variable as years, 1993 to 2004. However, I do not know what command or formula to use to generate the first difference for these rates. Can anyone offer some guidance? Thanks
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