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Best Practice Makes Perfect

A collaboration with Domino developers about how to do it and how to get it right in Domino

My Sprint bill has a new feature; since we have two phones, they helpfully suggest how we could split the bill between the phones. Here's their suggestion for this month:

  Splitting your bill? Here's our suggestion*:  
Charges
Taxes
Additional Sprint Charges
Total
(763) xxx-yyyy
$64.24
$5.54
$2.61
$72.39
(763) xxx-zzzz
-$3.25
$0.77
$0.95
-$1.53





  How did we calculate these suggestions?

  (Step 1) We added together charges like monthly recurring charges, overage charges, purchases and taxes for each individual subscriber.

  (Step 2) Then we added all account charges and taxes and divided the total account charges by the number of subcribers [sic] on the account.

  (Step 3) Finally, we added the individual subscriber charges from step 1 to the split account charges from step 2 to calculate the suggested split accounts.

Thank you, Sprint! I don't owe anything for my cell usage -- my wife pays the whole bill and owes me $1.53 besides. Not enough for a latté, but it's a start.

This is obviously wrong. So obvious, that you have to wonder whether they did any testing on this new feature. I think about all the people who might have wrong answers printed on their bills that are less obviously wrong. Sprint is doing these customers a disservice.  Some may never catch on -- others might notice something fishy after a few months, and have to go back through their old bills -- assuming they kept them -- to manually recalculate the split and adjust accordingly. Fun!

Even if the figures looked plausible, I'd want to decide whether I agree with their algorithm.  But the description is too vague to be useful. It doesn't mention how it takes into account the relative minutes-usage of the two lines, for instance; maybe it doesn't.

In fact, what makes for a fair split? Is there a single answer that fits everybody? These are complicated bills.  There's a base amount which doesn't vary, there might be equipment charges (say I bought a new phone holder, which I should pay for 100%), there might be odd credits (this month there's a "settlement invoice credit" -- do we divide that based on this month's usage or should we average over some period of time?), or mysterious one-time charges.  If you go over your prepaid minutes there's a per-minute charge, and so on. But let's keep it simple for the sake of an example. Say the bill is just the base amount this month. We pre-pay (let's say) 500 minutes. I use 1 minute. My wife uses 299. Does this mean I pay 1/300th of the bill and she pays the rest? That doesn't seem fair. It's worth something just to have service, in case of need, even if you make no calls. Each phone should contribute some minimum amount for that, and some additional amount depending on usage. But the exact amount of the minimum is something the people involved have to negotiate. At least, I don't see an obvious answer that would fit everyone. And consider the usage-based portion. Suppose we decide we each pay 1/4, and divide the rest based on usage. The bill is $60 -- we each pay at least $15. If I use 1 minute, and my wife uses 2, she pays $35 and I pay $25? Wow, that was an expensive minute! If I use 100 and she uses 300, the ratio seems fairer, but clearly there has to be some division in the payment for the unused minutes, the exact details of which have to be negotiated.

I could go on in this vein for some time.  The point is that Sprint decided to take on an impossible task -- there's no one way to split the bill that everybody would consider fair -- and they did it extremely poorly besides. Maybe there's some algorithm that many of their subscribers would consider close enough to fair that the difference is too small to make it worth manual calculation. This isn't it, and even if it were, it's not described precisely enough to let people decide whether that's pretty close to the way they would do it.

If they wanted to support people who split the bill, might it not be better to just pull together in one place, all the numbers people might want to plug into their own formula? But apparently nobody at Sprint thought this through. Now they can say, "We help you figure out how to split your bill!" and whether they do so in a way that's actually useful, is immaterial, because potential customers don't get to see it until they've already signed a contract.

One thing I can say based on the scenarios I've been running through my head while writing this -- it's just as well we don't split our bill. What a load of bother!

Andre Guirard | 2 January 2009 12:37:00 PM ET | Home, Plymouth, MN, USA | Comments (0)

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