# Re: [R] Estimating QAIC using glm with the quasibinomial family

From: Kunio takezawa <r.otasuke_at_gmail.com>
Date: Thu, 08 May 2008 09:15:46 +0900

R-users
E-mail: r-help_at_r-project.org

>but I was specificly interested in calculating QAIC and QAICc from
>a glm fitted with the "family=quasibinomial" option.

If you use "family=quasibinomial(link = "logit")" in glm(), the program will be:

function ()
{

xx <- c(1,2,3,4,5,6,7,8,9,10)
yy <- c(1,0,1,0,0,1,0,1,1,1)
data1 <- data.frame(x=xx, y=yy)
out1 <- glm(y~x, data=data1, family=quasibinomial(link = "logit"))    print(out1)
aic0 <- out1\$aic
print("aic0")
print(aic0)

dev1 <- out1\$deviance
aic1 <- dev1+ 2*2
print("aic1")
print(aic1)

c1 <- 2.5
qaic1 <- dev1/c1+ 2*2
print("qaic1")
print(qaic1)
}

The result is:
Call: glm(formula = y ~ x, family = quasibinomial(link = "logit"), data = data1)

Coefficients:

```(Intercept)            x
-0.7300       0.2131

Degrees of Freedom: 9 Total (i.e. Null);  8 Residual
Null Deviance:      13.46
Residual Deviance: 12.63        AIC: NA
[1] "aic0"
[1] NA
[1] "aic1"
[1] 16.63054
```

[1] "qaic1"
[1] 9.052216

As you pointed out, glm() does not output the value of either AIC or QAIC.
You are supposed to calculate those values. I guess that it is because AIC is not
appropriate for this case, and the concept of QAIC has not been authorized yet.

K. Takezawa

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