ANOVA & Tukey


I'm doing my research, studying on the effect of pH (acid-base) and ionic strength (IS, salt ions) on denaturation temperature (Td) of protein, temperature which protein is destroyed. I used 3 different pH & IS levels. Therefore, there were 9 conditions. I used SPSS software to analyze my data. I used univariate analysis of variance to check for differences between Td. The output shows that there is no effect of the interaction between pH*IS (p = .717). For the main effect, the p-value of pH is 0.00 which is significant. and the p-value of IS is 0.066 which is not significant. However, after doing Tukey HSD & Bonferroni tests, they found significant differences between the means of Td at various IS levels. How could this happen? Why ANOVA told me that the effect of IS in not significant but Tukey HSD & Bonferroni tests told me opposite thing. How should I report?

Thanks in advance



you noted to that tukey is post hoc.
it is a very important matter, the first you should do Anova so if is not significant you shouldnot do post hoc.
i hope you will be succeed.