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>"I got very grumpy at an official graph of British teenage pregnancy rates that apparently showed they had declined to nearly zero. Until I realized that the b
by nonbel 11y ago
>"I got very grumpy at an official graph of British teenage pregnancy rates that apparently showed they had declined to nearly zero. Until I realized that the bottom part of the axis had been cut off, which made it impossible to visualize the (very impressive) 50% reduction since 2000."
Don't understand. I'd think not truncating the y-axis would make it more difficult to see a change.
>"I thought people would know that 3 out of 100 is equal to 3% is equal to 0.03. But they are very different!"
Don't understand. Those numbers are all the same by definition.
- tome 11y ago> >"I thought people would know that 3 out of 100 is equal to 3% is equal to 0.03. But they are very different!" > Don't understand. Those numbers are all the same by definition. They are ways of representing that same number but people respond to them differently.
- nonbel 11y agoSo the numbers are not very different, just erroneously perceived to be different (according to psychologists). I guess it isn't as odd as I thought after skimming, but I still don't like it.
- golergka 11y agoNumbers are not different mathematically. Written representations of numbers are different psychologically.
- Absentinsomniac 11y agoIf you start a graph at like 50 on the y axis it's easy to make data look more pronounced. The official graph showed they dropped to "zero", presumably a bigger difference than 50%. Like it would look like the line dropped to zero, but really the graph started higher than zero on the y axis to begin with. Idk about the second one.
- nonbel 11y agoThanks. I didn't think that he meant they were exaggerating the change, but you seem to be correct.
- azneo 11y agoSee this: https://twitter.com/d_spiegel/status/707860293683126272 https://twitter.com/d_spiegel/status/707860293683126272
- cjlars 11y agoA good guideline for whether to truncate a y-axis or not is that the conclusion that a reasonable and knowledgeable researcher would draw after looking at the data should be clearly implied based on a quick cursory glance at the chart. If the chart implies an unreasonable conclusion based on a cursory glance, then it might be said to be misleading. A chart's purpose is to convey information quickly, not to convey information precisely -- for that, a table is often better. In the example, the true effect is that there was a ~50% decrease, which is newsworthy and interesting in and of itself. Yet, intentionally or not, the chart implies a ~100% decrease based on a quick glance, and so fails to highlight the conclusion that a reasonable person would draw from the underlying data. In this case, I would say a y-axis from 0-60% would be appropriate.