Call:
glm(formula = bids ~ . + I(size^2), family = poisson, data = TakeoverBids)
Coefficients:
Estimate Std. Error z value Pr(>|z|)
(Intercept) 0.986060 0.533920 1.847 0.06477 .
legalrestyes 0.260146 0.150959 1.723 0.08484 .
realrestyes -0.195660 0.192631 -1.016 0.30976
finrestyes 0.074030 0.216522 0.342 0.73242
whiteknightyes 0.481382 0.158870 3.030 0.00245 **
bidpremium -0.677696 0.376737 -1.799 0.07204 .
insthold -0.361991 0.424329 -0.853 0.39361
size 0.178503 0.060022 2.974 0.00294 **
regulationyes -0.029439 0.160568 -0.183 0.85453
I(size^2) -0.007569 0.003122 -2.425 0.01532 *
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
(Dispersion parameter for poisson family taken to be 1)
Null deviance: 121.862 on 125 degrees of freedom
Residual deviance: 88.615 on 116 degrees of freedom
AIC: 389.9
Number of Fisher Scoring iterations: 5
logLik(tb_p)'log Lik.' -184.9483 (df=10)
## dispersion tests
## Cameron and Trivedi (2013, p. 185)
AER::dispersiontest(tb_p, alternative = "less", trafo = 2)
Underdispersion test
data: tb_p
z = -1.1863, p-value = 0.1177
alternative hypothesis: true alpha is less than 0
sample estimates:
alpha
-0.06829684
AER::dispersiontest(tb_p, alternative = "less", trafo = 1)
Underdispersion test
data: tb_p
z = -3.0281, p-value = 0.001231
alternative hypothesis: true alpha is less than 0
sample estimates:
alpha
-0.3175595
## visualization of underdispersion
if(require("topmodels")) {
rootogram(tb_p)
qqrplot(tb_p, range = c(0.05, 0.95))
}

Min. 1st Qu. Median Mean 3rd Qu. Max.
-3.22537 -0.71963 -0.07505 0.00000 0.37182 5.57238
Min. 1st Qu. Median Mean 3rd Qu. Max.
-1.606458 -0.521439 -0.068443 0.001562 0.297047 3.026831
Min. 1st Qu. Median Mean 3rd Qu. Max.
-2.27187 -0.55501 -0.06922 -0.08986 0.28720 2.39771
df AIC
tb_p 10 389.8967
tb_hp 20 358.9549
if(require("topmodels")) {
rootogram(tb_hp)
qqrplot(tb_hp, range = c(0.05, 0.95))
}
