R Under development (unstable) (2026-08-27 r90452 ucrt) -- "Unsuffered Consequences"
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> require(bbmle)
Loading required package: bbmle
Loading required package: stats4
> x <- 0:10
> y <- c(26, 17, 13, 12, 20, 5, 9, 8, 5, 4, 8)
> d <- data.frame(x,y)
> fit <- mle2(y~dpois(lambda=ymax/(1+x/xhalf)), start=list(ymax=25,xhalf=3),data=d)
> fit2 <- mle2(y~dpois(lambda=(x+1)*slope), start=list(slope=1),data=d)
> BIC(fit)
[1] 62.0039
> BIC(fit,fit2)
     df      BIC
fit   2  62.0039
fit2  1 228.2046
> 
> ## GH #35: nobs() method was missing for mle2 objects, so BICtab()/ICtab()
> ## failed outright (fell back to nobs.default -> "no 'nobs' method is
> ## available"), and even when it worked, an explicit 'nobs' argument to
> ## ICtab(type="BIC") was silently ignored (only AICc/qAICc used it).
> stopifnot(identical(nobs(fit), 11L))
> 
> bictab1 <- BICtab(fit, fit2, mnames=c("fit","fit2"), base=TRUE)
> stopifnot(isTRUE(all.equal(bictab1$BIC, c(BIC(fit), BIC(fit2)))))
> 
> ## explicit nobs override should change the BIC value (e.g. for binomial
> ## data where the correct sample size is the number of trials, not rows)
> bictab2 <- BICtab(fit, mnames="fit", base=TRUE, nobs=1000)
> expected <- -2*c(logLik(fit)) + attr(logLik(fit),"df")*log(1000)
> stopifnot(isTRUE(all.equal(bictab2$BIC, expected)))
> stopifnot(!isTRUE(all.equal(bictab2$BIC, bictab1$BIC[1])))
> 
> proc.time()
   user  system elapsed 
   1.31    0.20    1.50