if I had just one shot to share an important ideahere it is. No joke. Look

RATIOS DEMAND LOG SCALE

the coolest non-trivial example when a log Y-axis is required to represent ratios

going from 50 in ~1988 to 25 in ~2001 is as bad as going from 100 in 1970 to 50 in ~1988

Fascinating how the data story is changing – the seeming recent plateau is no longer there. And log *is* the *right* way to represent the nature of the data and tell the story.

The plots above are made by @CedScherer using @WWF data via @OurWorldInData https://ourworldindata.org/grapher/global-living-planet-index?country=~Freshwater

Here are the two tweets by @CedScherer prepared for today's #30DayChartChallenge https://twitter.com/CedScherer/status/1380223704811106308

RATIOS appear whenever you divide something by something else of a similar class/nature. Ratios are dimensionless. The most common "hidden" case is time series standardisation when some year is taken for 100%, like 1970 in the example above

The thing is: the story (the shape of the line) will change depending on the arbitrary choice of the year taken as 100%. We divide all other years by this standard effectively creating *ratios*

I genuinely believe this is *the* most common #dataviz issue

It also often becomes a problem in statistical analysis – log transformation of the ratios are required before regression/correlation analysis is performed on the data

[side note]
It's even more important than the ones coming right after:
– #RotateTheDamnPlot
– #IncreaseTheDamnFont

The realisation of this simple data visualization and analysis rule literally took me ages of slow mind walk: from odds ratios through other explicit ratios to the "hidden" ones like here. Even color bars in the plot legends should be log transformed if they colorcode ratios!

I lost track how many times I've pointed this out

RATIOS DEMAND LOG SCALE

The idea to write a blog post on visualizing ratios correctly lives in my head and to-do list for well over a year now

Let me use this thread to legally bind myself to write it up soon