I need help in calculating the goodness of fit for a Poisson model. The online literature on it is quite scarce, so if you have any useful articles and links I would appreciate it very much.

Here is how the table looks like from SPSS. The outcome variable is a count of patents a company has.

model http://img827.imageshack.us/img827/1655/screenshot20130606at124.png


marked as duplicate by kjetil b halvorsen, mdewey, Reinstate Monica, gung - Reinstate Monica regression Aug 30 '18 at 18:46

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    $\begingroup$ Three possibilities: (1) the data is hugely overdispersed relative to the Poisson; (2) your model is not picking up the a major cause of variation in the mean, so your conditional distribution is a mixture of very different nearly-Poissons, making it look overdispersed compared to a better model; or (3) it's actually overdispersed relative to the Poisson and you're not picking up the mean well, making it worse $\endgroup$ – Glen_b Jun 6 '13 at 3:41
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    $\begingroup$ @Scortchi I am not convinced that's necessarily a duplicate. Here we have (at least potentially) a Poisson regression model - what may effectively be a mix of Poissons with different parameters; a univariate goodness of fit test would no use for that. The OP should clarify, but I don't want to close too hastily. $\endgroup$ – Glen_b Jun 21 '13 at 0:45
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    $\begingroup$ @Glen_b You're quite right - it looks a lot more like this. $\endgroup$ – Scortchi - Reinstate Monica Jun 21 '13 at 8:18
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    $\begingroup$ @Scortchi ... yes, I think that's basically a duplicate. $\endgroup$ – Glen_b Jun 21 '13 at 8:27
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    $\begingroup$ The image link is now dead, making this question impossible to answer. $\endgroup$ – Reinstate Monica Aug 30 '18 at 16:06