====== chi square test ======
<code>
# read the data
df <- read.csv("https://goo.gl/j6lRXD")
# summarize data to table 
table(df$treatment, df$improvement)
             
              improved not-improved
  not-treated       26           29
  treated           35           15

</code>

<code># Chi-sq test
chi <- chisq.test(df$treatment, df$improvement, correct=FALSE)
chi  
	Pearson's Chi-squared test

data:  df$treatment and df$improvement
X-squared = 5.5569, df = 1, p-value = 0.01841
</code>

<code>> summary(chi)
          Length Class  Mode     
statistic 1      -none- numeric  
parameter 1      -none- numeric  
p.value   1      -none- numeric  
method    1      -none- character
data.name 1      -none- character
observed  4      table  numeric  
expected  4      -none- numeric  
residuals 4      table  numeric  
stdres    4      table  numeric  
> </code>

<code> round(chi$expected,2)
             df$improvement
df$treatment  improved not-improved
  not-treated    31.95        23.05
  treated        29.05        20.95

round(chi$observed,2)
             df$improvement
df$treatment  improved not-improved
  not-treated       26           29
  treated           35           15
</code>

<WRAP box help>
Do chi-square test as explained in [[:chi-square test]] explanation. 
</WRAP>

{{tag> statistics r "chi-square test"}}