While I appreciate your reply, which confirms what I suspected, I cannot say that it is entirely satisfactory. The operating system and hardward have not changed in the year since this program last ran on SAS v9.2; or at least it hasn't changed in a way that affects any of the other millions of calculations we do every day. So I am confiedent that is not a factor. As for looking at the unformatted values for comparison, that is part of the problem: nlmixed formats these values (pvalue6.4) in the ods output we are using. If there is a way to change or turn off this format, or otherwise get to the raw values, I have not been able to find it. So although I can accept your explanation as likely (and we have no choice but to accept the v9.4 output as it is), I still don't know whether the algorithm adjustment was in nlmixed or the pvalue format. The only thing I could find in the documentation that mentioned differences between releases was for pvalue, indicating that there might be small differences if option DECIMALCONV is set to STDIEEE. In our case, the option is set to COMPATIBLE, but in fact changing it does not change this particular output. But thank you anyway.
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