Chi-squared approximation may be incorrect Please I need your help. I am trying to run this data using R but it throws an error message 'Chi-squared approximation may be incorrect.' Is something wrong with my data?
> Hypotension_tab1 <- table(VR1$'Hypotension during treatment?',VR1$'Maximum tolerated dose of Vericiguat (mg)')
> Hypotension_tab1
     
      2.5 5 7.5 10
  No    5 4   1  1
  Yes   1 4   0  1

> chisq.test(Hypotension_tab1)

    Pearson's Chi-squared test

data:  Hypotension_tab1
X-squared = 2.404, df = 3, p-value = 0.4929


Warning message:
In chisq.test(Hypotension_tab1) :
Chi-squared approximation may be incorrect


Fisher's is primarily designed for a 2x2 table but for this example it should work fine. You could also use simulate.p.value = FALSE in chisq.test() which will generate 2000 tables with the same marginal values (row and column sums) to compare with your observed data. Both approaches show that the original Chi Square p-value is an underestimate:
chisq.test(tbl)
# 
#   Pearson's Chi-squared test
# 
# data:  tbl
# X-squared = 2.404, df = 3, p-value = 0.4929
fisher.test(tbl)
# 
#   Fisher's Exact Test for Count Data
# 
# data:  tbl
# p-value = 0.5984
# alternative hypothesis: two.sided
chisq.test(tbl, simulate.p.value=TRUE)
# 
#   Pearson's Chi-squared test with simulated p-value (based on 2000 replicates)
# 
# data:  tbl
# X-squared = 2.404, df = NA, p-value = 0.6802

Notice that the last approach gives the most conservative estimate of the p-value. Since none of them approach .05. The best conclusion is that the sample is too small to suggest a significance difference.
