A round-up of our favourite charts of 2020 December 21, 2020 at 05:09PM

As with so many things in 2020, though, coronavirus has ruined our plans. Without doubt the data team has produced some outstanding covid-19-related data journalism, from a prescient piece on February 3rd about how airlines fare during pandemics, through covid-adjacent takes on booms in baby-making and bread-baking, to our interactive charts and maps tracking the spread of the virus and excess mortality around the world. But we felt that readers might want a break from relentless covid coverage at this time of the year. So we have selected a handful of our favourite non-covid articles that you may have missed. We’ll reveal a new one every day this week.

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In October we asked whether it is better to be a poor pupil in a rich country than the reverse. Gathering income data is easy but comparing test scores around the world is harder than it sounds. Although pupils in the rich world mostly take one of a handful of big international exams, many developing countries rely on regional tests.

A new working paper attempts to get around this lack of apples-to-apples comparison. Its authors set an exam for around 2,000 Indian pupils that included both questions from the leading international tests and ones taken from smaller exams. Using answers from the same pupils on the same day to questions from different tests, they built a statistical model they called a “Rosetta Stone” that allows them to translate scores from a range of regional exams into an equivalent mark on other common international tests.

As the chart shows, students in rich countries from less well-off families do indeed perform better than richer children in poor countries, but income levels within countries can make a big difference too. And as we wrote this week, school closures caused by the pandemic will only widen this gap.

In February, we analysed song data from Spotify for 30 countries around the globe. Using the streaming service’s “valence” algorithm—a formula that classifies how happy a song sounds on a scale from 0 to 100—we were able to identify the peaks and troughs of each nation’s musical mood. Most countries experience a dip in listening to happy-sounding songs in February and a sustained surge in July. But there were surprising regional differences. Lively Latin music seems to lift the mood of many South American countries all year round while Scandinavians have gloomier listening habits than the global average. A daily chart from the archives suggests that they make up for it at Christmas: one in every six songs streamed in Sweden and Norway in December 2016 was a festive tune; in Brazil, a country with a similar proportion of Christians, it was just one in 150.