The data exists for Christianity, and has a large enough sample of countries to look at for correlations. Would be interesting to see the results. The general point would hold, that simplistic generalizations require far more nuance.

Interpretation of “Islamic law” is subjective, and greatly influenced by place and time. You make some great points on how this metric is problematic. In the article we go into more detail about how this finding speaks more to political contexts than it does religious adherence. We thought to include it because it did stand out as an interesting finding, rather than exclude it, and it provided a means to discuss one of the many nuances involved. We also detail the socio-cultural challenges of selecting which factors to analyze (such as regular prayer), and which not to analyze (such as our excluding the practice of Ramadan and Hajj as well as Zakah).

How have you found “Islamic Law” interpreted within the context of the study? I’m assuming from the use of quote marks, it means a more overt and invasive enforcement, which is usually what happens when it is discussed specifically – otherwise it’s just “law”. If so, it’s not concerning that its support declines with increasing GDP; presumably high GDP correlates with education level, a kind of society that does not appreciate being forced into religious adherence vs a more voluntary growth kind of adherence. Maybe also a greater suspicion of why a good thing needs to be so propagandized.

I know in my own country it’s impossible to get an informed, impartial discussion among laypeople on the practicalities of Islamic law proposals and exactly what is proposed and how close is this version’s fidelity with the letter and intent of Shariah law, and whether all of them must be passed together, and exactly how and what must be in place to get it done within the bounds of the constitution, and what the expected effects are from doing it this way vs another. Yet many of these people have strong convictions in favour of “the Islamic law”, mainly because, well, how can a Muslim be against it? It’s like in an eco-conscious community, with a proposal for a total ban on plastics – it would likewise be a bit hard to get a practical discussion going on, exactly which kinds of plastics you mean, how does this way solve the problem you had in mind, what kind of preparation is required to transition from one system to another, etc etc. People have the tendency to believe the solution to a problem is just ‘one’ thing and that there’s just the one way to apply it everywhere. But systemic changes are not plug and play.