I’ve been dealing with this problem for quite a time. I’m running an experiment with plants growing them with Compost A and Compost B. I’ve been measuring the pH each day at the same time and keeping most variables constant. I have one month worth of data( i.e 30 measurements for 6 Compost A subjects and 30 measurements for Compost B subjects). To each subject I have substracted a reference measurement which is the pH before a plant is introduced, to allow me to calculate the “change” as times passes.
I want to show that the change in ph across the days vary with the compost used.
I tried to use a graph showing the coefficient of variation but had no luck since the changes in pH are positive and negative in the first days. I tried to use an absolute value CV but it doesn’t feel right.
I wanted a more robust method to demonstrate that the difference it’s more obviously as the time goes by. I was thinking of using ANOVA but I don’t know how well suited it is for this type of data. I thought of maybe doing longitudinal analysis but I’m not sure if 30 days is enough data.
Would love to hear some suggestions.