# How to report significance of factor levels shown in summary of glm?

The summary of my GLM shows day 12 of factor Date to be significant, but anova(model, test="Chisq") shows Date to be not significant overall. I know how to report the statistics from the Chisq table, but as I have z values in the summary table I am unsure how to report, or if I should report, that day 12 is significant.

Similarly when finding that Date is significant, how to report what specific dates seem to be important.

Lara

I have Fertility and Fecundity of female flies measured over 12 days. I want to check if there is a decline (or otherwise) in fertility/fecundity over this time.

Additionally, at day 13 females are mated (with a male from one of two different groups), and fertility and fecundity are measured until day 20. I want to use Date as a factor to identify significant peaks in fertility/fecundity i.e. after mating, and potential difference in peaks between groups.

Call:
glm(formula = dda$Fertility.Absolute ~ sqrt(dda$Fecundity) +
dda$Group + dda$Date + sqrt(dda$Fecundity):dda$Group + sqrt(dda$Fecundity):dda$Date,
family = poisson)

Deviance Residuals:
Min       1Q   Median       3Q      Max
-3.1397  -0.6786  -0.4797   0.3596   3.7588

Coefficients:
Estimate Std. Error z value Pr(>|z|)
(Intercept)                    -1.91501    0.51539  -3.716 0.000203 ***
sqrt(dda$Fecundity) 0.72372 0.12441 5.817 5.99e-09 *** dda$Group2                      0.19540    0.19230   1.016 0.309585
dda$Date4 0.18117 0.62648 0.289 0.772439 dda$Date6                      -0.28952    0.68983  -0.420 0.674706
dda$Date8 0.07111 0.60531 0.117 0.906480 dda$Date10                      0.19557    0.62232   0.314 0.753325
dda$Date12 0.79619 0.60710 1.311 0.189696 dda$Date14                      1.93702    0.53938   3.591 0.000329 ***
dda$Date16 0.75623 0.58296 1.297 0.194554 dda$Date18                     -0.05392    0.67805  -0.080 0.936618
dda$Date20 -0.26291 0.68841 -0.382 0.702530 sqrt(dda$Fecundity):dda$Group2 -0.07309 0.04822 -1.516 0.129583 sqrt(dda$Fecundity):dda$Date4 0.27388 0.17555 1.560 0.118734 sqrt(dda$Fecundity):dda$Date6 0.37684 0.22832 1.651 0.098836 . sqrt(dda$Fecundity):dda$Date8 0.13017 0.13861 0.939 0.347674 sqrt(dda$Fecundity):dda$Date10 0.04552 0.15345 0.297 0.766722 sqrt(dda$Fecundity):dda$Date12 -0.16593 0.14861 -1.117 0.264186 sqrt(dda$Fecundity):dda$Date14 -0.24864 0.12754 -1.949 0.051240 . sqrt(dda$Fecundity):dda$Date16 0.05496 0.14578 0.377 0.706170 sqrt(dda$Fecundity):dda$Date18 0.15439 0.19341 0.798 0.424715 sqrt(dda$Fecundity):dda$Date20 -0.02006 0.16314 -0.123 0.902161 --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 (Dispersion parameter for poisson family taken to be 1) Null deviance: 1327.36 on 359 degrees of freedom Residual deviance: 298.26 on 338 degrees of freedom AIC: 873.65 Number of Fisher Scoring iterations: 5 ### Analysis of Deviance Table Model: poisson, link: log Response: dda$Fertility.Absolute
Terms added sequentially (first to last)

Df Deviance Resid. Df Resid. Dev  Pr(>Chi)
NULL                                            359    1327.36
sqrt(dda$Fecundity) 1 893.88 358 433.48 < 2.2e-16 *** dda$Group                      1     0.03       357     433.45    0.8699
dda$Date 9 82.16 348 351.29 6.01e-14 *** sqrt(dda$Fecundity):dda$Group 1 0.07 347 351.22 0.7859 sqrt(dda$Fecundity):dda\$Date   9    52.96       338     298.26  2.97e-08 ***

• The first half of this is missing, i.e. what your scientific problem is, how Date features in your analysis, why you are treating it as a factor, etc. – Nick Cox Oct 15 '13 at 16:42
• Probably related – Affine Oct 15 '13 at 17:05