the Polity IV index of democracy does not appear as clear-cut in developing countries as some studies would have it (Xiaobo et al. 2018). With this caveat, and although it would be a stretch to interpret these studies causally, cross-national survey studies have provided an important basis and motivation for more (quasi-) experimental studies into the determinants of tax morale.

In observational studies, Pommerehne and Weck-Hannemann (1996) and Torgler (2005) show that Swiss cantons with more direct-democratic institutions also exhibit higher tax compliance. A similar implication is generated in the study by Alm and Torgler (2006) which finds that Switzerland and the U.S. have both strong direct democratic institutions and among the highest levels of tax compliance internationally. Much of the experimental work in this area has focused on laboratory settings, where many aspects of the environment are controlled by the researcher and the context and information environment can be manipulated more precisely. In one early landmark laboratory study Alm, Jackson, and McKee (1992) found that making decisions by voting increased tax compliance significantly in the lab. In their study of Swiss college students, Feld and Tyran (2002) argue that only notions of procedural legitimacy, which is generated by having laboratory subjects vote on a fine, can explain their finding that subjects comply more with a fine when it is voted on than when it is imposed. Importantly, while they do find a role for reciprocity (compliance with the fine is higher the more subjects voted for it) in explaining tax compliance, their argument goes beyond pure reciprocity to focus on _procedural fairness_ , or the belief that the method by which the decision was reached was fair.

More recently, Lamberton, De Neve, and Michael (2014) found evidence, also in a lab setting using American respondents, showing that simply allowing respondents to state their expenditure preferences reduced their use of a questionable tax loophole, thus raising compliance. They interpret this finding as reflecting a re-coupling of taxes with the services that they fund along the lines of the fiscal exchange hypothesis.

Finally, in a study based on Austrian laboratory subjects, Casal et al. (2016) find that a different type of “voice” also matters: subjects randomly assigned to a condition where they can make item-by-item decisions on which taxes to pay have higher total tax compliance than subjects randomly assigned to paying all taxes together.

However, while these types of studies credibly isolate causal effects, it is very difficult to get a sense of how much they hinge on the specific setting. First, while laboratory experiments do give researchers a large amount of control, they also tend to involve very specific types of respondents in artificial situations, and it is at least unclear how well they generalize to real-world behavior.

Second, and perhaps even more importantly, the vast majority of experimental studies of tax morale are implemented in rich Western democracies. Given that tax compliance is deeply interwoven with aspects of national tax and budget policy, political institutions and political culture, this raises important questions of the conditions, if any, under which we might expect to see the positive effects described above replicated elsewhere.

The importance of such issues of generalizability becomes especially visible when researchers use interventions tested in laboratory settings, and apply them to very specific real-world settings. For example, in a recent pioneering study, Kettle et al. (2017) randomly assign Guatemalan taxpayers to six different messages during their tax declaration, and fail to find any significant effects. Of course, in a sense, this is only surprising if one was previously led to believe that Guatemalan VAT tax payers should respond similarly to interventions as Swiss college students 5