ratioScales
Logarithmic axis scales can clearly communicate multiplicative changes; they can also confuse. ratioScales annotates logarithmic axis scales with tickmarks that denote proportional and multiplicative change simply and explicitly.
The main function in this package, scale_*_ratio(), is ggplot-friendly
and works similarly to existingscale_*_* functions from ggplot2
and scales.
Installation
You can install the development version of ratioScales from GitHub with:
# install.packages("devtools")
devtools::install_github("mikeroswell/ratioScales")Example
Consider exchange rates between US and Canadian dollars:
exch %>%
ggplot(aes(date, exRate, color = direction)) +
geom_point() +
scale_color_manual(values = hcl.colors(4, "Plasma")[c(1,2)]) +
labs(y = "exchange rate") 
Let’s see, relative to some baseline (1 April 2020), is the Canadian dollar gaining or losing ground against the US dollar, and by how much?
exch %>% ggplot(aes(date, exRate_scale, color = direction)) +
geom_hline(yintercept = 1, color = "black")+
geom_point() +
scale_color_manual(values = hcl.colors(4, "Plasma")[c(1,2)]) +
geom_hline(yintercept = 0.85
, color = hcl.colors(4, "Plasma")[1], linetype = 3) +
geom_hline(yintercept = 1.15
, color = hcl.colors(4, "Plasma")[2], linetype = 5) +
# FUNCTION FROM ggplot2
scale_y_continuous(breaks = seq(80, 130, 5)/100) +
labs(y = "proportional change in exchange rate") 
But this is strange! Somehow the Canadian dollar weakend by a maximum of 15% before rebounding, but the US dollar strengthened by much more than 15%. Maybe not the best way to think about this?
ratioScales provides “rational” alternatives. For example, using a “divMult” scale:
exch %>% ggplot(aes(date, exRate_scale, color = direction)) +
geom_hline(yintercept = 1, color = "black")+
# times and divided by 1.15; longdash
geom_hline(yintercept = 1/1.15, color = hcl.colors(4, "Plasma")[1], linetype = 5) +
geom_hline(yintercept = 1.15, color = hcl.colors(4, "Plasma")[2], linetype = 5) +
# times and divided by 0.85; dotted
geom_hline(yintercept = 1/0.85, color = hcl.colors(4, "Plasma")[2], linetype = 3) +
geom_hline(yintercept = 0.85, color = hcl.colors(4, "Plasma")[1], linetype = 3) +
geom_point() +
scale_color_manual(values = hcl.colors(4, "Plasma")[c(1,2)]) +
# FUNCTION FROM ratioScales
scale_y_ratio(tickVal = "divMult", n = 12, nmin = 12, slashStar = FALSE) +
labs(y = "multiplicative change in exchange rate") 
Prefer percentage differences? Also ok, if you use an appropriate scale:
exch %>% ggplot(aes(date, exRate_scale, color = direction)) +
geom_hline(yintercept = 1, color = "black")+
# times and divided by 1.15; longdash
geom_hline(yintercept = 1/1.15, color = hcl.colors(4, "Plasma")[1], linetype = 5) +
geom_hline(yintercept = 1.15, color = hcl.colors(4, "Plasma")[2], linetype = 5) +
# times and divided by 0.85; dotted
geom_hline(yintercept = 1/0.85, color = hcl.colors(4, "Plasma")[2], linetype = 3) +
geom_hline(yintercept = 0.85, color = hcl.colors(4, "Plasma")[1], linetype = 3) +
geom_point() +
scale_color_manual(values = hcl.colors(4, "Plasma")[c(1,2)]) +
# FUNCTION FROM ratioScales
scale_y_ratio(tickVal = "percDiff") +
labs(y = "percentage difference in exchange rate") 