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Growth model with no intercept |
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I have a variable measured four times age 14, 16, 18 and 20 I have done a series of GCM to find the best one. in particular the first model tested was a no-growth model (only intercept) The second was a linear model. In this model we fixed the factor loadings on the slope at 0, 1, 2, 3. The third model examined a non-linear growth. The chi square difference test revealed that the best model is the non linear one. yt = n0 + n1 xt + et ; with x3 and x4 as parameters to be estimated; Now a referee told me that it is crucial that the authors evaluate the following submodel: yt = n1 xt + et, with x2, x3, and x4 as parameters to be estimated and x1 =1. this is the input i have wrote: s by MD14@1 MD16*1 MD18*2 MD20*3; md16 with md18 (4); md14 with md16 (2); md18 with md20 (2); MD14 (8); MD18 (10); model female: md16 with md18 (5); md14 with md16 (1); md18 with md20 (1); MD14 (8); MD18 (10); Is this model nested with the linear one? and is the requested model make sense? Thank you |
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This looks like a growth model with no intercept growth factor. I am not sure if it is identified and it does not make sense to me. I would ask the referee to give more information. |
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thank you , this model is identified with a good fit. The reviewer cited the work of Meredith and Tisak (1990). My problem is that I don't think it is nested with the other models i tested. Is it right? |
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Even if the model is nested, with an implied zero variance of the intercept growth factor, difference testing cannot be used because a variance of zero in on the border of the admissible parameter space. |
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