Chris Jackson’s Formula (for When to Test For Application Compatibility)

OK, so it’s not as famous as e=mc2, but here is the rule I apply for when to test an application for app compat.


You should test your applications when:

cost failure × probability failure > cost testing


You should otherwise not bother to test your applications – just fix them reactively through your standard helpdesk processes. From a business perspective, it just doesn’t make sense to pay more to avoid a risk than it would to just march straight into it and have to pay that fine. I mean, if I offered you a “get out of traffic court free” card for $1000, and traffic tickets cost $100, how many would you buy from me?

Comments (3)

  1. Alex says:

    Now let's only hope the one who has to do the maths does it right 🙂

  2. Mike says:

    Unfortunately this is the Microsoft business model for new O/S releases. Its good enough – let's see where it's broke by letting the customers find the bugs. Imagine if your automobile manufacturer thought the same thing about your family's safety…would you buy from that same manufacturer again? Its lucky that MS has the monopoly it does because this model does not work in ANY other business environment. I certainly would not suggest this to my C-level decision makers.

  3. cjacks says:

    @Mike – I don't believe your analogy to cars is completely accurate here. I'm not speaking of the OS itself. If you find a bug in the OS, we own that the same way a car manufacturer might have to repair or recall a car if either an individual or systematic bug were found. Rather, the better analogy for what I'm speaking of is a warranty on what you choose to do with the car. If you plan to put a 98-year-old former Indy car champion in the car and expect to win the Indy 500, then you may be disappointed that your driver is no longer up to the task. If you have a written procedure to start your car by turning the camshaft clockwise on the front of the car, you may find that algorithm is no longer as helpful as it was on your Model-T. If it's your responsibility to ensure that your driver and operations manuals still apply to your new car, then you should take a risk-driven approach to determining which it makes financial sense to proactively investigate. (In these examples, you may decide that not enough people read the manual to make it worth replacing, yet it might be mission critical to get a driver capable of winning a race if you run a racing team, or vice versa if you run a team responsible for creating car manuals.)

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