[R] mimic SPSS contingency table results
Petr PIKAL
petr.pikal at precheza.cz
Thu Jul 8 10:59:04 CEST 2010
Dear all
Seems that puzzles always come in packs. I was asked to help with some
statistics in blood analysis. (You can not refuse your wife's asks :-).
She has contingency table for values IgVH mutation and ZAP expression. I
can do chi-square test (in R) and get a results, and with some literature
I can try explain them. However she found an article in which they use
SPSS and use gamma-squared test?? Resulting p-value is different from R
chi square and seems to be close to fisher.test.
They also get percentages for sensitivity and specificity with 95%
confidence interval for these percentages and here I am lost. Also
something called positive or negative predictive value is something I do
not know how to get from contingency table.
Is it possible to get this in R? Where to look?
Here are data
mat <- matrix(c(22,7,9,15), 2,2)
>From that matrix they get:
positive statistical association between columns (IgVH mutation status)
and rows (ZAP expression) with p=0.005
which is close to fisher.test
They also get sensitivity and specificity for prediction 62.5% (CI: 41-84)
and 76% (CI: 59-93) respectively and positive predictive value 68% (CI:
46-90) and negative predictive value 71% (CI: 53-89)
It seems that dividing observed value by marginal value is close but
***how I can get confidence intervals***?
22/31 resp. 15/22 or 22/29 resp. 15/24
Any hint or explanation would be greatly appreciated.
Best regards
Petr
chisq.test(mat)
Pearson's Chi-squared test with Yates' continuity correction
data: mat
X-squared = 6.4582, df = 1, p-value = 0.01104
fisher.test(mat)
Fisher's Exact Test for Count Data
data: mat
p-value = 0.006152
alternative hypothesis: true odds ratio is not equal to 1
95 percent confidence interval:
1.391323 20.407944
sample estimates:
odds ratio
5.057521
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