Subscribe Bookmark RSS Feed

ANCOVA - Is it appropriate to use a categorical variable with only two datapoints?

ssda

Community Member

Joined:

Jan 26, 2012

My dataset is a stability dataset where I am looking at the degradation of a purity measurment (dependent variable) of multiple batches (categorical variable) over time (covariate).  I have data from a total of 7 batches.  Three of the batches have a purity measurement from four timepoints and 3 of the batches have a purity measurement from only two timepoints.

I want to assess the slope of all of the batches, but the batches with only two timepoints will have slopes that have no error.  Should I exclude the batches with only two timepoints?  Is in inappropriate to include them?   I need a real statisticians point of view, because I just dabble and this is dataset is confusing to me.