I find this study problematic because it fails to take into account that life satisfaction is highly dependent on the exact moment when the respondents answers

I find this study problematic because it fails to take into account that life satisfaction is highly dependent on the exact moment when the respondents answers the questionnaire even if 10 years apart. If I had a bad day and it so happened that it was the day where I was supposed to fill in a form on my life satisfaction, my answer would probably be very biased regardless if I was religious or not. It also fails to take into account that not all religions are based on happiness meaning that life satisfaction in this world is not the be all and all. An example is Islam. In Islam this worldly life is considered as a test. So you're going to be tested with hardship, afflictions and so on. There is also the concept of this being cyclical. After hardship comes ease. (not really cyclical in the sense that hardship comes because you had some ease before it but more like tuples of (hardship, ease) coming your way one after the other) If you keep steady while you're being tested you'll be rewarded with paradise or/and a period of ease in this life. Otherwise if you disobey Allah's commandements and die upon disbelief (You did not repent sincerely while you were still alive.) you'll likely go to hell. Here it would be understandable to the believer that their life will not be all roses.