I'd argue that the zero value should always be shown. Otherwise you get different impressions of the rate depending how you scale and subset the Y axis.
This is not a good practice at all. Do you think atmospheric CO2 charts should show 0? How about daily temperature reading for human body temperature? Should daily stock tickers all start at 0?
Why is 0 magical?
Adding 0 to the vast majority of plots shows that data at an unnatural scale that can obscure genuinely important information. Human body temperature readings on a scale from 0 to 107F would make all the important information hard to see.
A much better rule is that charts should have reasonable bounds based on knowledge of the system. For human temperature in F anything less that 95 and greater than 107 basically mean you're dead. For processes in nature good points are some delta - the lowest record to delta + highest recorded. For things like daily stock prices, a few standard deviations each way from historic volatility works.
The dogma that charts should all start at 0 is complete nonsense and tries to side step reasoning about you data. Yes scales can be used to misrepresent data, but forcing 0 to the axis does not solve this.
Yes. Charts are communication devices. Any "rules" for charts should be seen like similar "rules" for essays or emails: good advice that almost always gives a satisfactory result when followed. Reliable paths for infrequent authors.
But what matters most in charts is the same thing that matters most with writing: pick one major point and stick to it (if you're really good or can't avoid it, maybe a couple points). This also explains why a lot of dual-axis charts don't work: the author explains two sets of data that aren't even measured on the same scale and then leaves the reader to connect them and understand the meaning of that connection. You can't be sure the reader will end up at the point you wanted to make.
That's not to say a dual-axis chart is always the wrong choice. Just that, if you start making one, stop and ask if there isn't a better way to show the data. Same with pie charts.
Fahrenheit is not an absolute scale, so there is nothing special about 0F, you're right about that. As for your other two examples (atmospheric CO2 and stock tickers)... Yes, the scale should start at 0. Why shouldn't they?
PheonixPharts|1 year ago
Why is 0 magical?
Adding 0 to the vast majority of plots shows that data at an unnatural scale that can obscure genuinely important information. Human body temperature readings on a scale from 0 to 107F would make all the important information hard to see.
A much better rule is that charts should have reasonable bounds based on knowledge of the system. For human temperature in F anything less that 95 and greater than 107 basically mean you're dead. For processes in nature good points are some delta - the lowest record to delta + highest recorded. For things like daily stock prices, a few standard deviations each way from historic volatility works.
The dogma that charts should all start at 0 is complete nonsense and tries to side step reasoning about you data. Yes scales can be used to misrepresent data, but forcing 0 to the axis does not solve this.
vharuck|1 year ago
But what matters most in charts is the same thing that matters most with writing: pick one major point and stick to it (if you're really good or can't avoid it, maybe a couple points). This also explains why a lot of dual-axis charts don't work: the author explains two sets of data that aren't even measured on the same scale and then leaves the reader to connect them and understand the meaning of that connection. You can't be sure the reader will end up at the point you wanted to make.
That's not to say a dual-axis chart is always the wrong choice. Just that, if you start making one, stop and ask if there isn't a better way to show the data. Same with pie charts.
yau8edq12i|1 year ago
lupire|1 year ago