Association Rules - Importance

I understand Mr. MacLennan's explanation provided at http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=282651&SiteID=1 and appreciate the time he took to explain how importance works. However, like the user with username "sang", I also ran the data in BI 2005 and got the same results listed by the aforementioned user. I did this using the following data:







donut
muffin

y
y

y
y

y
y

y
y

y
y

y
y

y
y

y
y

y
y

y
y

y
y

y
y

y
y

y
y

y
y

n
y

n
y

n
y

n
y

n
y

etc.

The rule muffin -> donut has an importance of -0.105302438, which is not the same as Mr. MacLennan's results. I tried switching the roles of a and b in a -> b and using different bases on the logarithms. I don't get the result of -0.105302438 with any of these. I also tried to calculate importance with a small data set I have and can't get the results using Mr. MacLennan's explanation with that data set either. Any thoughts on the descrepancy?