I have two data set. 1. developmental stages (1, 2, 3, etc.) based on the body characteristics (morphology) of larvae of an insect species 2. the number of days after hatch

Then, I want to see if each develomental stage based on the body characteristics can predict (or have any association with) the number of days after hatch. The data set of "the number of days after hatch" has normal distribution and homovenous variance. So I used "stages" as x values and "the number of days" as y values and did a regression analysis. However, the developmental stages were set by myself based on the body characteristics of each larva, which is of course not really objective. (All stages are distinct enough to separate each other though.) Someone told me that because "stages" were subjectively set, I cannot use any parametric tests and I should choose non-parametric correlation test rather than regression. Is this true???

Also, I wanted to see if there is any difference in the number of days after hatch among stages and did ANOVA. However, with the same reason above, I was told to change from ANOVA to a non-parametric test.

Please help me if someone has any idea about this as I don't have anyone to ask around. I will really appreciate your help!!

Many thanks.

-fsms