hk0316 Exercise-1

#匯入資料、檢視資料

dta <- ToothGrowth

dim(dta)

## [1] 60  3

str(dta)

## 'data.frame':    60 obs. of  3 variables:
##  $ len : num  4.2 11.5 7.3 5.8 6.4 10 11.2 11.2 5.2 7 ...
##  $ supp: Factor w/ 2 levels "OJ","VC": 2 2 2 2 2 2 2 2 2 2 ...
##  $ dose: num  0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 ...

顯示Supplement OJ和Supplement VC，在len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="boxplot 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

由於變異數不相等，採用Welch’s t-test

由於P值=0.06>0.05 ，故使用不同維他命的兩組，沒有達到統計上顯著差異。

常態分布情形(畫長條圖)

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