ToothGrowth

將ToothGrowth資料命名為dta

dta <- ToothGrowth

ToothGrowth資料有60列3行

dim(dta)

## [1] 60  3

變項名稱為：length、supplement、dose

names(dta)

## [1] "len"  "supp" "dose"

從頭顯示資料 (由supplement VC起頭)

head(dta)

##    len supp dose
## 1  4.2   VC  0.5
## 2 11.5   VC  0.5
## 3  7.3   VC  0.5
## 4  5.8   VC  0.5
## 5  6.4   VC  0.5
## 6 10.0   VC  0.5

從尾顯示資料 (由supplement OJ起頭)

tail(dta)

##     len supp dose
## 55 24.8   OJ    2
## 56 30.9   OJ    2
## 57 26.4   OJ    2
## 58 27.3   OJ    2
## 59 29.4   OJ    2
## 60 23.0   OJ    2

顯示Supplement OJ和Supplement VC的mean

aggregate(len ~ supp, mean, data=dta)

##   supp      len
## 1   OJ 20.66333
## 2   VC 16.96333

Length & Supplement的盒狀圖

lattice::bwplot(len ~ supp, data=dta, 
                main="Distribution of length at different supplements",
                xlab="Supplement (OJ & VC)", ylab="Length")

不同的supplement是否對於牙齒的生長有差異(t-test)

t.test(len ~ supp, data = dta)

## 
##  Welch Two Sample t-test
## 
## data:  len by supp
## t = 1.9153, df = 55.309, p-value = 0.06063
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  -0.1710156  7.5710156
## sample estimates:
## mean in group OJ mean in group VC 
##         20.66333         16.96333

multicon::diffPlot(len ~ supp, data=dta, grp.names=c("OJ", "VC"),
 xlab="Supplement", ylab="Length")

常態分配檢視

with(dta, lattice::histogram(~ len | supp, type="density", xlab="Supplement"))

Q：Investigate if type of vitamin supplement(x) has an effect on teeth growth(y) in guinea pigs.

According to t-test, two kinds of supplements have a different effect on teeth growth.