Researchers, many of them, count and measure things. Here is an example:
“Are Christian/religious people poor tippers?” Michael Lynn [pictured here] and Benjamin Katz, Journal of Applied Social Psychology, Volume 43, Issue 5, May 2013, pp. 928–935. (Thanks to investigator Dan Griliopoulos for bringing this to our attention.)
The authors, at Cornell University School of Hotel Administration and at HCD Research, respectively, explain:
“A web-based survey was used to assess the relationships of religious faith and frequency of church attendance with tipping under conditions of good and bad service. Results indicated that Jews and those with no religion tipped more than Christians and members of other religions, but that the vast majority of Christians tipped at or above the normative 15% of bill size. Worship frequency also significantly interacted with service quality such that the tips of those who frequently worship vary with service quality less than the tips of those who worship less frequently. The practical implications of these results for service workers and restaurants or other service businesses with a large religious clientele are discussed.”
Here’s detail from the study:
BONUS (unrelated): A study co-authored by Charity and Faith:
“Study protocol for promoting respectful maternity care initiative to assess, measure and design interventions to reduce disrespect and abuse during childbirth in Kenya,” Charity Ndwiga, Faith Mbehero, et al., BMC Pregnancy and Childbirth 2013, 13:21.