Misleading bar charts #3

We keep discussing axis layouts and the problematic cases of non-zero baselines (in bar charts). Here is another example from the city of Dresden. Dresden is a really pretty place and it is always worth coming for a visit. With the below chart, the city wanted to showcase that each year new record tourist numbers are recorded.

Truthful bar chart

Now, since this isn’t the first time we discuss baselines, you should immediately spot that a rise from around 200,000 to 300,000 isn’t even close to a tripling of number as the bar length visually suggests. And overall, the bar-length does not actually even represent the increase at all. It rather seems that their lengths were chosen to fit an imaginary linear increase. I re-plotted the bar chart with a zero-baseline. Lo-and-behold, the rising number of tourist is still visible, but clearly not nearly as record-worthy.

Dresden_visitors_1 — Truthful bar chart reporting Dresden tourist data.

Really truthful bar charts

For each chart, we should not only think about baselines but ask: where do the numbers come from? And, do we see the complete dataset? In this case, the data was collected by the city of Dresden, which should be a reasonably good source for basic statistical data (all data is here: https://www.dresden.de/de/leben/stadtportrait/statistik/wirtschaft-finanzen/tourismus.php).

The image however circulated in 2017 – three years after the last data-point shown! Now, if you know that since the end of 2014 Dresden is plagued by very prominent weekly demonstrations of right-wing activists, having no data after 2014 is alarming. In the local science and business community the problems are very evident: we have a clear drop in international scientists applying and accepting jobs in the city! I therefore went to the Dresden city website to get the data for the subsequent years and this confirmed what I suspected: tourist numbers no longer rose, instead, they even dropped!

Dresden_visitors_2 — Dresden tourists 2010-2018. Show all the relevant data – leaving out years might be misleading.

Line or bar chart?

Time trends are usually more visible in line charts. Indeed, the drop of tourist numbers since 2014 is very apparent in a line chart, and even more so when we leave out the zero-baseline, which somewhat flattens the data (note: in line charts leaving out zero-baseline is ok and sometimes even necessary!).