Deafness in Dalmatians: Does sex matter?

Abstract

Recent studies on the prevalence of deafness in Dalmatians have reported vastly different gender effects on the prevalence. The diverse conclusions in these reports cover all possibilities, higher prevalence in males, no difference between genders and higher prevalence in females. Much of this confusion about the effect of gender on the Dalmatian's hearing status is due to the unsatisfactory statistical interpretation of the available data. Careful analysis of a large ( n=1234) composite database on Dalmatians in the UK has provided a reliable assessment of the effect of gender on deafness. The overall rate of deafness in the tested Dalmatians was 18.4%, of which 13.1% were unilaterally deaf and 5.3% were bilaterally deaf. The overall deafness in females (21.1%) was significantly higher ( p=0.014) than that in males (15.5%). In all subsets of the full dataset [subsets obtained by partitioning by testing locations, colour (black or liver spots), parental hearing status (normal or untested) and time (year of test)], the prevalence was higher in females compared with males. Unlike other studies, the confounding of the gender effect with other factors, particularly the parental hearing status, was avoided in the large, composite UK study. Because dogs from the same litter might be correlated with respect to their deafness status, the data were analysed further to take the random litter effect into account. This further emphasised the difference between genders. We believe that the reason for the prevailing confusion in the literature is that the unwary referees and readers give the same amount of credence to `not significant' results from small scale studies as they give to significant results from large scale studies and do not always recognize the absence of sound statistical methods.