levels(data$year)[levels(data$year) == '11'] <- 'year ^ {2011}'
levels(data$year)[levels(data$year) == '12'] <- 'year ^ {2012}'
p <- ggplot(data1, aes(x=month))
+ geom_line(aes(y=value.x, color=method.x))
+ facet_grid(. ~ year,labeller = label_parsed)
