Moody's used to publish probability of default estimates from their Moody's EDF model, but they have temporarily discontinued it. I understand that the Moody's EDF model is closely based on the Merton model, so I coded a Merton model in Excel VBA to infer probability of default from equity prices, face value of debt and the risk-free rate for publicly traded companies.
However, the probabilities of default that I get from the Merton model are drastically different from the Moody's EDF model. Generally they're extremely high or extremely low and the ranking of the same firms is totally different. I understand that Moody's uses an empirical distribution while Merton uses a normal distribution in order to calculate these probabilities - is this the only source of the discrepancy?
If I want to accurately reproduce Moody's EDF probabilities of default, what approach should I use? Since I can't reproduce their empirical distribution, is this pointless?
I'd be happy to post my code if anybody is interested.