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summary(cars)
##      speed           dist       
##  Min.   : 4.0   Min.   :  2.00  
##  1st Qu.:12.0   1st Qu.: 26.00  
##  Median :15.0   Median : 36.00  
##  Mean   :15.4   Mean   : 42.98  
##  3rd Qu.:19.0   3rd Qu.: 56.00  
##  Max.   :25.0   Max.   :120.00

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library(vcd)
library(vcd)
head(Arthritis)
##   ID Treatment  Sex Age Improved
## 1 57   Treated Male  27     Some
## 2 46   Treated Male  29     None
## 3 77   Treated Male  30     None
## 4 17   Treated Male  32   Marked
## 5 36   Treated Male  46   Marked
## 6 23   Treated Male  58   Marked
mytable<- xtabs(~Treatment + Improved, data= Arthritis)
addmargins(mytable)
##          Improved
## Treatment None Some Marked Sum
##   Placebo   29    7      7  43
##   Treated   13    7     21  41
##   Sum       42   14     28  84
chisq.test(mytable)
## 
##  Pearson's Chi-squared test
## 
## data:  mytable
## X-squared = 13.055, df = 2, p-value = 0.001463
library(vcd)
mytable <- xtabs(~Improved + Sex, data= Arthritis)
addmargins(mytable)
##         Sex
## Improved Female Male Sum
##   None       25   17  42
##   Some       12    2  14
##   Marked     22    6  28
##   Sum        59   25  84
chisq.test(mytable)
## Warning in chisq.test(mytable): Chi-squared approximation may be incorrect
## 
##  Pearson's Chi-squared test
## 
## data:  mytable
## X-squared = 4.8407, df = 2, p-value = 0.08889