Thank you for the opportunity to reply to Dr Rakhshan’s letter regarding the apparent statistical “issues and ambiguities” with our research.
The estimation of power for this study was not simply based on a pilot study, but also based on the only other study carried out using MRI to assess condylar position/displacement, and where displacements of 1 mm were detected. More importantly, is Dr Rakhshan actually advising the readership that mean (absolute) differences of 0.141 mm (ranging from 0.01 to 0.36 mm) in the glenoid fossae are something of a clinical health concern? Should we have actually adjusted the detection of differences to 0.1 mm? Would this have been clinically relevant?
Repeated-measures ANOVA can be used to assess the variability of techniques. We also agree that with smaller samples a nonparametric test like the Friedman could have also been used, but we used parametric methods.
In contradiction to the claims made by Dr Rakhshan, in our “Results” section, there is reference to the P values. All P values were lower than 0.05 and, as such, were not statistically significant. The Tukey was the post-hoc test to use if any significant differences were detected; however, there were none.
The underlying distribution was deemed normal, and as such, ANOVA was used. Variable results do not necessarily indicate nonnormal underlying distributions.
Condylar positions were discussed in relation to CO. Because the Roth power and CR bite registrations were supposedly capable of positioning condyles in the glenoid fossae in relation to CO, we discussed the differences in relation to CO.
We do not agree that lines 3 to 8 are unclear; they are in fact quite the opposite. If there was any significant positioning difference that was detectable, we would have found it, but we did not. This was more than safe to infer.
It appears that Dr Rakhshan has sadly and simply fixated his whole critique on his own interpretation of the statistics, claiming that our findings were unreliable or unsubstantiated. We are acutely aware that limitations do exist with any research. Our study simply and openly shows that the differences detected between the registrations were so small and highly variable that using certain bite registrations to accurately and predictably position condyles into specific locations in the glenoid fossae is not evidence based. Our findings are reliable and substantiated.