Sir,

I have a problem here while applying chisquare test to the following Data (
below the subject of this mail) ...when I wanted to test the significance
using three different free statistical packages, here R, EpiInfo and
OpenEpi.

*Only OpenEpi accepts the test based on Cochran's Recommendations. *
R says " chi squared approximation may be incorrect."
Does it mean the same as what EpInfo saying " Chi square is not valid"

Regards,
Dr. B. Manoj Aravind.

*Table for analysis*

                                  Number of STDs Identified
Type of Health worker     <2                    2 or >

ASHA                             39                    5
AWW                              22                    1
ANM                               1                     12

......................................
*In R the ouput was like this....*

> std<- cbind(c(39,22,1),c(5,1,12))
> std
     [,1] [,2]
[1,]   39    5
[2,]   22    1
[3,]    1   12
> chisq.test(std)

Pearson's Chi-squared test

data:  std
X-squared = 43.8055, df = 2, p-value = 3.074e-10

Warning message:
In chisq.test(std) : *Chi-squared approximation may be incorrect*

In EpInfo the output was this

            Analysis of Single Table
An expected cell is <5.  *Chi square is not valid.*
              Chi square = 43.81
              2 degrees of freedom
              P<0.00000000 <--
.....................................
In OpenEpi the output was like this

Single Table AnalysisVar 2 39 544Var 1221 2311213 621880   Chi Square for R
by C Table
------------------------------
  Chi Square=43.81Degrees of Freedom=2p-value= <0.0000001 Cochran recommends
accepting the chi square if: 1. No more than 20% of cells have expected < 5.2.
No cell has an expected value < 1. In this table: 17% of 6 cells have
expected values < 5.No cells have expected values < 1.  *Using these
criteria, this chi square can be accepted.*  Expected value = row
total*column total/grand total Rosner, B. Fundamentals of Biostatistics. 5th
ed. Duxbury Thompson Learning. 2000; p. 395

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