Hi All,

I'm fitting a logistic regression and I summed up the deviance and used a chi-square distribution to test over-dispersion with this code below:

2 Questions:

Q1: I'm getting a p-value < 0.05, so does this mean overdispersion id detected?

Q2: How does it impact my model coefficient? What should be my next step?

Thank you so much and have a wonderful day!

All the best,

Kathy

P.S. Here is the R code:

p_hat = predict(model_obj,newdata = model_obj$model, type = "response")

D = -2 * sum(p_hat * log(p_hat/(1-p_hat))+log(1-p_hat))

chi_sq_n = nrow(model_obj$model)

chi_sq_p = length(strsplit(Reduce(paste, deparse(model_obj$formula)), "[~+ ]+")[[1]])-1

chi_sq_df = chi_sq_n - chi_sq_p

chi_sq_pval = pchisq(D, df = chi_sq_df)

Where model_obj is a logistic regression object.