Mean and SD of Percent Tip (Along with Sample Size) at Each Level of Customer-rated Service Quality for Four Published Studies Bodvarsson and Lynn and Lynn and Graves Service Rating Gibson (1984) Grassman (1990) [a] (1996: Study 1) [a] 1 (poor) 8.
Contrary to Bodvarsson and Gibson's claims, the weakness of the tipping-service relationship in the existing literature is not just a reflection of restricted variability in service ratings.
First, they argue that ratings of service quality exhibit little variability and that this restriction of variability "biases" the size of the correlation between service ratings and tip amounts.
They argue that this restriction of variability in service ratings biases tests of the tipping-service relationship and that the relationship would be stronger if the bias were eliminated.
First, restrictions in the variability of service ratings affect the size of the tipping--service relationship only as measured in terms of variance explained.