Bad graph hunting
Much can go wrong when making data visualisations.
Creating graphs is a key way to communicate statistics. There are many steps to this process, and graphs have a grammar.
Studying bad examples is often a good way to learn. Through failure, gain insights into the means of success.
Google cards
The Google card for reported Covid-19 surveillance deaths is inaccurate. The rolling average calculation is incorrect.
Their graph treats non-reporting days as if those values were missing. Reported deaths on days the agency does not update are, by definition, zero. For 21st April 2022, the seven-day rolling average should be about 239. Surveillance deaths by date of report were, in those last three days: 682, 508, and 482.
Since the agency did not report on the other four days, those other figures are zero. To get the seven-day rolling average, we sum and divide by seven.
The Google graph performs a different calculation, averaging non-zero days. If their figures matched the UKHSA dashboard, the calculation would give about 557. These differences appear to arise…
