[Gretl-users] Fisher's Exact Test in gretl

[yinung at Gmail]

Dear all,

I notice that "xtab" command can do Fisher's exact test. I found that
fisher.test(.) in R (requires vcd package) also produces Fisher's exact
test results. Does anyone know the differences between gretl's and R's
Fisher's exact test?

I test the following data (which can be downloaded from
http://ibeif.files.wordpress.com/2012/12/fishertea.xls

obs real guess
1    1     1
2    1     1
3    1     1
4    1     2
5    2     2
6    2     2
7    2     1
8    2     2

In gretl, the following script

<hansl>
open http://ibeif.files.wordpress.com/2012/12/fishertea.xls
xtab real guess
</hansl>

produces the results:

Cross-tabulation of real (rows) against guess (columns)

       [   1][   2]  TOT.

[   1]     3     1      4
[   2]     1     3      4

TOTAL      4     4      8

Pearson chi-square test = 2 (1 df, p-value = 0.157299)
Warning: Less than of 80% of cells had expected values of 5 or greater.

Fisher's Exact Test:
  Left:   P-value = 0.985714
  Right:  P-value = 0.242857
  2-Tail: P-value = 0.257143

However, in gretl with the following R script

fisher.test(table(real,guess))

produces the different results:


    Fisher's Exact Test for Count Data

data:  table(real, guess)
p-value = 0.4857
alternative hypothesis: true odds ratio is not equal to 1
95 percent confidence interval:
   0.2117329 621.9337505
sample estimates:
odds ratio
  6.408309


Thanks

Yi-Nung Yang

Dear all,

I notice that "xtab" command can do Fisher's exact test. I found that fisher.test(.) in R (requires vcd package) also produces Fisher's exact test results. Does anyone know the differences between gretl's and R's Fisher's exact test?

I test the following data (which can be downloaded from http://ibeif.files.wordpress.com/2012/12/fishertea.xls

obs real guess
1    1     1
2    1     1
3    1     1
4    1     2
5    2     2
6    2     2
7    2     1
8    2     2

In gretl, the following script

<hansl>
open http://ibeif.files.wordpress.com/2012/12/fishertea.xls
xtab real guess
</hansl>

produces the results:

Cross-tabulation of real (rows) against guess (columns)

       [   1][   2]  TOT.
 
[   1]     3     1      4
[   2]     1     3      4

TOTAL      4     4      8

Pearson chi-square test = 2 (1 df, p-value = 0.157299)
Warning: Less than of 80% of cells had expected values of 5 or greater.

Fisher's Exact Test:
  Left:   P-value = 0.985714
  Right:  P-value = 0.242857
  2-Tail: P-value = 0.257143

However, in gretl with the following R script

fisher.test(table(real,guess))

produces the different results:


    Fisher's Exact Test for Count Data

data:  table(real, guess)
p-value = 0.4857
alternative hypothesis: true odds ratio is not equal to 1
95 percent confidence interval:
   0.2117329 621.9337505
sample estimates:
odds ratio
  6.408309


Thanks

Yi-Nung Yang