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I have samples of stories from three newspapers, all testing for the same proportion of stories with a certain characteristic.

The data I have is: np1=16.34%, np2=14.00%, np3=18.29%. I want to demonstrate whether or not there is a statistically significant difference between the three values.

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  • $\begingroup$ Are you asking what test to use? Do you have the actual counts w/ & w/o the characterstic. $\endgroup$ – gung Aug 30 '15 at 20:44
  • $\begingroup$ I have the counts and am looking for what test to use. I've only done quite basic stats before - enough to know how to do linear regression for some of my other tests but this is beyond me. $\endgroup$ – Harper Aug 30 '15 at 20:46
  • $\begingroup$ Possible duplicate (up to the "5 categories" rather than "3 categories"). $\endgroup$ – Glen_b Aug 30 '15 at 23:22
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You simply need to enter the values with the characteristic and without it into a table of counts. Then you can use the chi-squared test. Under the assumption that there are 10,000 stories from each newspaper, I demonstrate the idea below with R code:

x = rbind(c(1634, 1400, 1829),
          c(8366, 8600, 8171) )
as.table(x)
#      A    B    C
# A 1634 1400 1829
# B 8366 8600 8171
chisq.test(x)
# 
#  Pearson's Chi-squared test
# 
# data:  x
# X-squared = 67.937, df = 2, p-value = 1.769e-15
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  • $\begingroup$ AH! Thank you. I thought I was doing something to make it too hard for myself. Simple now! $\endgroup$ – Harper Aug 30 '15 at 22:53
  • $\begingroup$ You're welcome, @Harper. Why not register your account while you're here? You can find out how in the My Account section of our help center. $\endgroup$ – gung Aug 30 '15 at 22:56

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