library(MASS)
library(ggplot2)
library(dplyr)
##
## Attaching package: 'dplyr'
## The following object is masked from 'package:MASS':
##
## select
## The following objects are masked from 'package:stats':
##
## filter, lag
## The following objects are masked from 'package:base':
##
## intersect, setdiff, setequal, union
data("anorexia")
names(anorexia)
## [1] "Treat" "Prewt" "Postwt"
head(anorexia)
## Treat Prewt Postwt
## 1 Cont 80.7 80.2
## 2 Cont 89.4 80.1
## 3 Cont 91.8 86.4
## 4 Cont 74.0 86.3
## 5 Cont 78.1 76.1
## 6 Cont 88.3 78.1
tail(anorexia)
## Treat Prewt Postwt
## 67 FT 82.1 95.5
## 68 FT 77.6 90.7
## 69 FT 83.5 92.5
## 70 FT 89.9 93.8
## 71 FT 86.0 91.7
## 72 FT 87.3 98.0
#selecting ft
ft_data <- anorexia %>%
filter(Treat == "FT")
#dataframing
library(dplyr)
Prewt_ft <- anorexia %>%
filter(Treat == "FT") %>%
dplyr::select(Prewt)
Postwt_ft <- anorexia %>%
filter(Treat == "FT") %>%
dplyr::select(Postwt)
#add to data
Prewt_ft <- ft_data$Prewt
Postwt_ft <- ft_data$Postwt
hist(Prewt_ft, main = "Histogram of Before Treatment", xlab = "Pre-treatment weight", col = "pink")
hist(Postwt_ft, main = "Histogram of After Treatment", xlab = "After-treatment weight", col = "lightblue")
Prewt_ft_result <- shapiro.test(Prewt_ft)
Prewt_ft_result
##
## Shapiro-Wilk normality test
##
## data: Prewt_ft
## W = 0.98821, p-value = 0.9972
format(Prewt_ft_result$p.value, scientific = FALSE)
## [1] "0.9972153"
#normal distrubution
Postwt_ft_result <- shapiro.test(Postwt_ft)
Postwt_ft_result
##
## Shapiro-Wilk normality test
##
## data: Postwt_ft
## W = 0.83928, p-value = 0.007391
format(Postwt_ft_result$p.value, scientific = FALSE)
## [1] "0.007390658"
#not normal distribution
wilcox_test_result <- wilcox.test(Prewt_ft, Postwt_ft, paired = TRUE, exact = FALSE)
wilcox_test_result
##
## Wilcoxon signed rank test with continuity correction
##
## data: Prewt_ft and Postwt_ft
## V = 11, p-value = 0.002091
## alternative hypothesis: true location shift is not equal to 0
#there is a statistically significant difference between the weights of Before #Q-Q plot
#Q-Q plot
qqnorm(Prewt_ft)
qqline(Prewt_ft, col = "orange")
qqnorm(Postwt_ft)
qqline(Postwt_ft, col = "red")