Dial idol is primarily a way to use your computer's modem to dial the numbers for you.

It does collect data from the users and measure the percentage of busy signals. They then do some math on the busy signals that has to do with when they come in and various other factors to generate a predictive score.

It is not a scientific survey of all the idol's phone numbers. They do not get the same number of calls in for all idols. Some fan bases use dial idol more than others.

Allison's fan base always was big on dial idol. She often had way more votes cast for her through dial idol than other people. However her percentage of all calls made by dial idol that were busy signals was pretty low. So she got a lower score than someone who had many fewer fans using dial idol but the small number of people got huge numbers of busy signals.

The dialidol guy puts a fair amount of the raw data on the site, not just the final number his computer model throws out.