t-Test Assignment

library(haven)

## Warning: package 'haven' was built under R version 3.5.3

data1 <- read_sav("asthma_pefr.sav")

names(data1)

## [1] "age"      "drug_grp" "pefr"

is.factor(data1$drug_grp)

## [1] FALSE

#labeling the Drug Group 1 as A, 2 as B and 3 as C
data1$drug_grp <- factor(data1$drug_grp,
                         levels = c(1,2),
                         labels = c("A","B"))

# PURPOSE
# To find difference of mean PEFR between drug A and drug B

#############################################################

# Checking normality assumption via boxplot
plot(data1$drug_grp, data1$pefr,
     main = "Boxplot showing distribution of PEFR between Drug A and Drug B",
     xlab = "Drug Type",
     ylab = "PEFR")

#Checking equality of variance assumption
library(car)

## Warning: package 'car' was built under R version 3.5.3

## Loading required package: carData

## Warning: package 'carData' was built under R version 3.5.2

leveneTest(data1$pefr~data1$drug_grp, center = mean)

## Levene's Test for Homogeneity of Variance (center = mean)
##        Df F value Pr(>F)
## group   1  0.3686 0.5439
##       882

# Since p-value = 0.7947 > 0.05
# Variance is equal

#Independent t-Test
#using t.test()
t.test

## function (x, ...) 
## UseMethod("t.test")
## <bytecode: 0x0000000011efd008>
## <environment: namespace:stats>

#Hypothesis Statement
#H0: There is no significant difference on mean pefr between Grug A and B
#H1: There is a significant difference on mean pefr between Grug A and B

#Conducting independent sample t-test
tt <- t.test(data1$pefr~data1$drug_grp, var.equal = T)
tt

## 
##  Two Sample t-test
## 
## data:  data1$pefr by data1$drug_grp
## t = 5.4058, df = 882, p-value = 8.311e-08
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  24.21958 51.83121
## sample estimates:
## mean in group A mean in group B 
##        359.0501        321.0247

library(broom)

## Warning: package 'broom' was built under R version 3.5.3

z <- tidy(tt)
View(z)


#Decision Rule
#Since p-value=8.310744e-08 < a=0.05, we reject Ho

#Conclusion
#There is a significant difference on mean pefr between Grug A and B