Different font faces and sizes within label text entries in ggplot2

Question

I am building charts that have two lines in the axis text. The first line contains the group name, the second line contains that group population. I build my axis labels as

Answer 1

I found another simple solution below:

require(ggplot2)
Treatment <- rep(c('T','C'),each=2)
Gender <- rep(c('Male','Female'),2)
Response <- sample(1:100,4)
test_df <- data.frame(Treatment, Gender, Response)

xbreaks <- levels(test_df$Gender)
xlabels[1] <- expression(atop(bold(Female), scriptstyle("POP1")))
xlabels[2] <- expression(atop(bold(Male), scriptstyle("POP2")))

hist <- ggplot(test_df, aes(x=Gender, y=Response, fill=Treatment,
stat="identity"))
hist +
  geom_bar(position = "dodge") +
  scale_y_continuous(limits = c(0, 100), name = "") +
  scale_x_discrete(label = xlabels, breaks = xbreaks) +
  opts(
    axis.text.x = theme_text(size = 12)
  )