Extending our previous research, we are now showing how emotions in books could correlate with systemic factors, such as the status of an economy (PLOS ONE, 2014). In our main experiment, we use a composite economic index that represents unemployment and inflation through the years, titled as Economic Misery (EM), and correlate it against a Literary Misery index (LM), that represents the composite emotion of Sadness minus Joy in books. We observe the best correlations, when EM is averaged over the past decade (see Fig. 1(a) & 1(b)); correlations increase for the period of 1929 (Great Depression) onwards. Interestingly, we get very similar results for books written in American English, British English and German when compared to their local EM indices (i.e. for the US, UK and Germany respectively). For more methodological details, a better presentation of all the results and an interesting discussion, where we argue that causation may be the reason behind this correlation, I have to point you to the actual paper.
Bentley A.R., Acerbi A., Ormerod P. and Lampos V. Books average previous decade of economic misery. PLOS ONE, 2014.