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According to the WinBUGS manual the gamma distribution is defined by:

dgamma(r,mu)

However, what is r? Is it the shape, scale or rate parameter? I'm pretty new to statistics and googling didn't really help. Above that in most explanations I've found ris usually not mentioned. It's either k, theta, beta or alpha.

Gerome Bochmann
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  • I'd guess `r` is the shape & `mu` is the mean. Should be documented somewhere, as there's no one 'right' way to parametrize a distribution. You could simulate some values to check. In JAGS it's shape then rate. – Scortchi - Reinstate Monica Feb 26 '14 at 15:15
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    Some details given in this excellent answer on the differences between BUGS and R distribution syntax... http://stats.stackexchange.com/a/5564/13267 – guyabel Feb 26 '14 at 15:19
  • Wow, then it's completely different from what I thought. I thought mu was the mean since gamma distributions can also be defined by the mean. – Gerome Bochmann Feb 26 '14 at 15:30
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    The density function *is* given in the [WinBUGS user manual](http://www.mrc-bsu.cam.ac.uk/bugs/winbugs/manual14.pdf). – Scortchi - Reinstate Monica Feb 26 '14 at 15:37
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    This question appears to be off-topic because it is about software documentation, not Statistics. – Scortchi - Reinstate Monica Feb 26 '14 at 15:38
  • Yes, being a beginner in statistics, I still have a habit of just ignoring formulas a lot. Thanks for pointing me to it. I didn't even notice the density function. I'll try to reword the question. – Gerome Bochmann Feb 28 '14 at 09:28

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