Breaking every limb is very painful

February 20, 2013

(This article was originally published at Junk Charts, and syndicated at StatsBlogs.)

This Financial Times chart is a big failure:


Look at the axis. Usually a break in the axis is reserved for outliers. If there is one bar in a bar chart that extends way beyond the rest of the data, then you would sever that bar to let readers know that the scale is broken. Here, the designer broke every bar in the entire chart. It's as if the designer knows we'll complain about not starting the chart at zero -- so the bars all start at zero except they jump from zero to 70 right away.


Trifecta_checkupThe biggest issue with this chart is not its graphical element. It's the other two corners of the Trifecta checkup: what is the question being asked? And what data should be used to address that question?

The accompanying article complains about the dearth of HB1 H-1B visas for technical talent at businesses. But it never references the data being plotted.

It's hard for me to even understand what the chart is saying. I think it is saying that in Bloomington-Normal, IL, 94.8 percent of its HB1 H-1B visa requests are science related. There is no way to interpret this number without knowing the percentage for the entire country. It is most likely true that HB1 H-1B visas are primarily used to recruit technical talent from overseas, and the proportion of such requests that are STEM related is high everywhere. In this sense, it's not clear that the proportion of HB1 H-1B requests is a useful indicator of the dearth of technical talent.

Secondly, it is highly unlikely that the decimal point is meaningful. Given the highly variable total number of requests across different locations, the decimal point would represent widely varying numbers of requests.

I'd prefer to look at absolute number of requests for this type of analysis, given that Silicon Valley has orders of magnitude more technical jobs than most of the other listed locations. Requests aren't even a good indicator of labor shortage. Typically HB1 H-1B visas run up against the quota sometime during the year, and companies will stop requesting new visas since there is no chance of getting approved. This is a form of survivorship bias. Wouldn't it be easier to collect data on the number of vacant technical jobs in each location?



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