In what might portend some particularly gloomy literature in the 2020s, a new study has found a "dramatic" increase in the use of words expressing misery and unhappiness in books written during the 1980s.

Academics at universities in Bristol and London analysed more than five million books digitised by Google, looking at how frequently words denoting different moods were used. They divided their "mood" words into six categories – anger, disgust, fear, joy, sadness, surprise – with words falling into the "sadness" category ranging from "repent", "regret" and "rue" to "depress", "dismay" and "dispirit". These findings were used to develop a "literary misery" index reflecting mood in English-language books through most of the 20th century.

Literary misery was highest in the 1940s, they found, with the 1980s narrowly in second place, and the 1920s in third. Their research, published yesterday in PLOS ONE, found that an increase in frequency of miserable language in these decades correlated to the economic misery of the respective previous decades.

"Economic misery coincides with WW1 (1918), the aftermath of the Great Depression (1935) and the energy crisis (1975). But in each case, the literary response lags by about a decade," said co-author Dr Alberto Acerbi. "It looked like western economic history," said lead author of the study Professor Alex Bentley of the University of Bristol, "but just shifted forward by a decade."

Bentley suggested the "decade effect" is reflective of "the gap between childhood when strong memories are formed, and early adulthood, when authors may begin writing books".

"Book authors are drawing on their past experiences over a certain time period. They may have been teenagers during a recession or depression and then started publishing books in their twenties, or perhaps just generally writers of any age are drawing upon experiences over the last decade," he said. "Consider for example, the dramatic increase of literary misery in the 1980s, which follows the 'stagflation' of the 1970s. Children from this generation who became authors would have begun writing in the 1980s." Granta's 1983 list of the best young British novelists included Amis - who would publish Money in 1984 - Ian McEwan, Graham Swift, Pat Barker and Salman Rushdie.

The academics' literary misery index was plotted against an average of US and UK economy misery indices (the sum of inflation and unemployment rates), with the robustness of the results checked against an analysis of books written in German, "where the 20th-century economy was different, but [the results] still correlate[d] in the same way with German mood word equivalents", said Bentley.

"We were still very cautious about spurious correlations at this point but then we found virtually the same results for German economic versus literary misery," said co-author Paul Ormerod. "The results suggest quite clearly that, contrary to postmodern literary theory, literature serves a purpose. It informs people about the human condition, and the content adapts to the conditions of the time."

The authors predicted an increase in "literary misery" for the decade ahead, following the financial crisis of 2008. "Given the current era of recession and consequently the increased unemployment figures in most western countries … we may expect a relative increase of sad versus joyful words in the scripts across the next 10 years," said co-author Dr Vasileios Lampos.

"If our pattern continues, we can expect an increase in literary misery over the decade following the onset of the recession, but the point to make is that this is a statistical increase in 'mood words' over a massive sample of English books, fiction and non-fiction. So for me it's more like a shift in the zeitgeist rather than an increase specifically in depressing reads," added Bentley.