Week7

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library(MASS)

library(MASS)
data(anorexia)
summary(anorexia)

##   Treat        Prewt           Postwt      
##  CBT :29   Min.   :70.00   Min.   : 71.30  
##  Cont:26   1st Qu.:79.60   1st Qu.: 79.33  
##  FT  :17   Median :82.30   Median : 84.05  
##            Mean   :82.41   Mean   : 85.17  
##            3rd Qu.:86.00   3rd Qu.: 91.55  
##            Max.   :94.90   Max.   :103.60

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

ft<-anorexia[anorexia$Treat=="FT",]
weight<-c(ft$Prewt, ft$Postwt)
time<-c(rep("Before",nrow(ft)),rep("After",nrow(ft)))
ft_long<-data.frame(time,weight)
head(ft_long)

##     time weight
## 1 Before   83.8
## 2 Before   83.3
## 3 Before   86.0
## 4 Before   82.5
## 5 Before   86.7
## 6 Before   79.6

str(ft_long)

## 'data.frame':    34 obs. of  2 variables:
##  $ time  : chr  "Before" "Before" "Before" "Before" ...
##  $ weight: num  83.8 83.3 86 82.5 86.7 79.6 76.9 94.2 73.4 80.5 ...

hist(ft$Prewt,
     main="Weight Before Trearment",
     xlab="Weight")

hist(ft$Postwt,
     main="Weight After Treatment",
     xlab= "Weight")

diff<-ft$Postwt-ft$Prewt
shapiro.test(diff)

## 
##  Shapiro-Wilk normality test
## 
## data:  diff
## W = 0.95358, p-value = 0.5156

t.test(ft$Postwt, ft$Prewt, paired=TRUE) # 같은 환자의 치료 전후 몸무게를  비교하는 대응표본,차이값이 정규분포 만족

## 
##  Paired t-test
## 
## data:  ft$Postwt and ft$Prewt
## t = 4.1849, df = 16, p-value = 0.0007003
## alternative hypothesis: true mean difference is not equal to 0
## 95 percent confidence interval:
##   3.58470 10.94471
## sample estimates:
## mean difference 
##        7.264706