A Possible Problem with 4 Year Memberships

Buying a membership in the BC Liberals is for a four year term.   This longer term leads to a small problem I had not factored into looking at the leadership race, people move on a regular basis and do not update their addresses.  There are likely a large number of people that party has lost contact with but are still on the membership rolls.   So how many might it be?

I am assuming that Liberal party members tend to more likely to be home owners, older and wealthier than the average in the province.   Then using Stats Canada figures I can make an educated guess at how many people are likely to have moved in any given year.  The number I come up with is 10% per year.  

I do not know the details of the 35,000 members of the party before the race started - specifically how long they had been members.   I can estimate that about 10,000 to 12,000 people joined the party in the run up the the 2009 election because they were supporting someone seeking a Liberal nomination.   I am going to round this up to 15,000 to account for people that joined/renewed at the time of the election.   This leaves me with 20,000 members that got their membership at some other point in time.  I splitting them 75% per election and 25% post election.

Someone that has been a member for one year has a 10% chance of having moved, 2 years a 18% chance of having moved, 3 years a 25% of having moved, and 4 years at 30%.    Using this numbers I come to 7000 or so members that have moved since they joined the party.

So how many of them made sure the party had their correct address?  I suspect only half, but that is purely a guess.   What I end up with is something on the order of 3500 BC Liberal members that the party has lost contact with but are still on the membership rolls.   

Lower pre-leadership race membership is bad for George Abbott.