chapter: 8 効果量の変換

後で加筆。

8.1 統計量から効果量への変換

8.1.1 t -> d

set.seed(123)
A <- rnorm(100, 60, 10)
B <- rnorm(100, 50, 10)
# t to d
res.st <- t.test(A, B)
cohens_d(A, B)

## Cohen's d |       95% CI
## ------------------------
## 1.27      | [0.97, 1.58]
## 
## - Estimated using pooled SD.

t_to_d(res.st$statistic[1], res.st$parameter) #近似値

## d    |       95% CI
## -------------------
## 1.28 | [0.97, 1.59]

dhat <- 2*res.st$statistic[1]/sqrt(res.st$parameter)

8.2 効果量から効果量への変換

8.2.1 d <-> r

# Converting Between Indices of Effect Size -------------------------------
# d to r
group <- rep(c(0, 1), each=100)
set.seed(123)
A <- rnorm(100, 50, 10)
B <- rnorm(100, 60, 10)
dat <- data.frame(group=group, outcome=c(A, B))

cor(dat) #点双列相関

##             group   outcome
## group   1.0000000 0.3939704
## outcome 0.3939704 1.0000000

d <- cohens_d(dat$outcome[group==1], dat$outcome[group==0])$Cohens_d
r <- cor(dat$group, dat$outcome)
d_convert <- r_to_d(r)
r_convert <- d_to_r(d)