[R] chisq.test using amalgamation automatically (possible ?!?)

From: Mohammad Ehsanul Karim <wildscop_at_yahoo.com>
Date: Sun 26 Jun 2005 - 20:00:15 EST


Dear List,

If any of observed and/or expected data has less than 5 frequencies, then chisq.test (Pearson's Chi-squared Test for Count Data from package:stats) gives warning messages. For example,

x<-c(10, 14, 10, 11, 11, 7, 8, 4, 1, 4, 4, 2, 1, 1, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1)
y<-c(9.13112391745095, 13.1626482033341,

12.6623267638188, 11.0130706413029, 9.16415925139016,
7.47441794889028, 6.03743388141852, 4.85350508692505,
3.89248001363859, 3.11803140037476, 2.49617540962629,
1.99774139023269, 1.5985926374167, 1.27909653584089,
1.02341602646530, 0.818828097315106,
0.655132353196336, 0.524159229418155,
0.418022824890164, 0.335528136508225,
0.268448671671046, 0.214779801990545,
0.171840507806838, 0.137485729582785,

0.109999238967747, 0.0880079144684513,
0.070413150156564)

Chi.Sq<-sum((c(x[1:7], sum(x[8:9]), sum(x[10:11]),

sum(x[12:27]))-c(y[1:7], sum(y[8:9]), sum(y[10:11]),
sum(y[12:27])))^2/c(y[1:7], sum(y[8:9]),
sum(y[10:11]), sum(y[12:27]))) # using amalgamation
pchisq(Chi.Sq, df=9, ncp=0, lower.tail = FALSE, log.p = FALSE) # result being 0.8830207

but chisq.test(x,y) gives the following output with incorrect df:

        Pearson's Chi-squared test

data: x and y
X-squared = 216, df = 208, p-value = 0.3373

Warning message:
Chi-squared approximation may be incorrect in: chisq.test(x, y)

Is there any way that we can use directly chisq.test without having warning message in such cases (that is, using amalgamation conveniently so that we don't have to check each elements if they are less than 5 or not - the whole process being automatic, may be by means of programming)?

Any hint, help, support, references will be highly appreciated.
Thank you for your time.


Mohammad Ehsanul Karim

Web: http://snipurl.com/ehsan
ISRT, University of Dhaka, BD


                

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