evidence: Likewise, a repeated-measures ANOVA for the factors TIME (pain ratings for insufflation 1 to 4) and GROUP (CO2 or air) yielded no significant main effect for TIME (F1.3,63.3 = 2.039; p = 0.153), but significant results for both the main factor GROUP (F1,47 = 4.438; p = 0.041) and the interaction term TIME*GROUP (F2.6,121.2 = 3.3; p = 0.029).
intervention: continuous nasal insufflation of CO2
comparator: placebo
outcome: TIME (pain ratings for insufflation 1 to 4)