Hi All, I am working on re-analyzing per a reviewers request.
The goal of the project was to determine if the presence of predatory fishes caused female crabs to delay the release of larvae. Number of releases were recorded at three time periods: 1 hour before the simulated tide, 3 hours after the simulated tide and 6 hours after the tide. Predators were introduced at high tide and removed just following the 3 hour observation. Thus we have two categorical variables with three levels each. Time: pre-introduction, after introduction and after removal. Predator: no-predator, predator of adults and predator of larvae.
The number of females was not consistent between trials so my initial method was to use the SRH extension of the Kruskal wallace test to examine the percent of of larvae released.
A reviewer suggested that I use a GLM with a binomial distribution and logit link to analyze the larval release patterns. I used Crawley's book to analyze the data based on proportions. See code below. The problem I am running into is that the model is not including the predator control and interaction is excluding the predator control and the introduction time periods. Is this just the nature of using a binomial distribution (and/or our small sample size) or is there a way to force R to include all the factors and run all the interactions?
Thanks, Leif N=GLM$NumFemale-GLM$NumFemaleRelease y=GLM$NumFemaleRelease rv <-cbind(y,N) > model1=glm(y~GLM$Time*GLM$Treatment-1,family=binomial) > summary(model1) Call: glm(formula = y ~ GLM$Time * GLM$Treatment - 1, family = binomial) Deviance Residuals: Min 1Q Median 3Q Max -1.6024 -0.7146 -0.4284 -0.2512 3.9885 Coefficients: Estimate Std. Error z value Pr(>|z|) GLM$TimeAfterIntroduction -1.8289 0.2297 -7.963 1.68e-15 *** GLM$TimeAfterRemoval -3.6571 0.5064 -7.222 5.14e-13 *** GLM$TimePreIntro -5.0626 1.0029 -5.048 4.46e-07 *** GLM$TreatmentPlanktivore -0.0123 0.3211 -0.038 0.969 GLM$TreatmentPredator -0.1589 0.3311 -0.480 0.631 GLM$TimeAfterRemoval:GLM$TreatmentPlanktivore 0.5339 0.7132 0.749 0.454 GLM$TimePreIntro:GLM$TreatmentPlanktivore 0.6561 1.2708 0.516 0.606 GLM$TimeAfterRemoval:GLM$TreatmentPredator -0.1791 0.8399 -0.213 0.831 GLM$TimePreIntro:GLM$TreatmentPredator 1.7496 1.1496 1.522 0.128 --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 (Dispersion parameter for binomial family taken to be 1) Null deviance: 1720.2 on 270 degrees of freedom Residual deviance: 258.3 on 261 degrees of freedom AIC: 378.23 Number of Fisher Scoring iterations: 6 T -- Leif K. Rasmuson Doctoral Candidate Oregon Institute of Marine Biology Phone: (253)961-1763 E-Mail: rasmu...@uoregon.edu
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