Hi, I'm trying to fit a growth model to consumer willingness to pay estimates for increasing amounts of a good (e.g, 1 oz, 2 oz, 3 oz, 4 oz and 5 oz). To eliminate widely varying estimates, we gave everyone the same price level for 1 oz. and had them price the remaining 4 levels.
When I fit a growth model on the 5 observations, I run into the problem that there is no variance on X1 (the estimate for 1 oz.), which was intended. Any way to circumvent the problem (besides excluding that variable)?