What A Prediction Is And What It Is Not: Part II

Thanks to DAV for reminding me of a clarification. See yesterday’s comments. This post is mostly bookkeeping. Tomorrow we do more examples.

Sometimes, in contracts as in predictions, certain “unexpected turns of events” are agreed to, both before and after the fact, as negators of the prediction or contract. We might agree that rain-outs negate the baseball prediction and make it void. We need this “out” because the prediction had an explicit date and time which, if we did not create this “escape clause”, would have made the prediction a bust (the Tigers did not in fact score more runs on the stated date and time).

An unexpected turn of events isn’t considered a prediction failure when the parties (the statement) agree beforehand that “given there are no unexpected turns of events” as part of evidence. This is, of course, ambiguous, and we often find parties in contracts disputing (after the fact) whether the event that caused the prediction to fail was really “unexpected” or not.

We are finally at the meat: A prediction is a statement, conditional on clear provisos, about an event that can be empirically verified. Or “in principle” empirically verified. Not all predictions are verified: criminal trials come to mind. The jury, taking into account many provisos, rules guilty or not, which is a prediction of an event that might never be verified. Predictions are thus not just of events that happen in the future; but of events that are not yet known to the provisos; that is, evidence which forms the conditions of the prediction must not include the evidence “the event obtained” or “the event did not obtain”; for then the prediction is a circularity. For criminal trials this implies the jury does not start out assuming, and then continue to hold the assumption, “the guy did it” or “the guy is innocent.” Guilt or innocence is what they are trying to predict (prove).

Now if after the fact people disagree that the prediction failed or succeeded it is usually the “clear provisos” that are argued over and disputed, no matter how sharply the provisos seem to have been defined. Well, human nature and all that. It usually one side who says, “Conditions A are what the ‘clear provisos’,” meant while the other side says, “Obviously, conditions B are what the ‘clear provisos’ meant.”

Given conditions (or interpretation) A and the clear provisos, the prediction is either verified or not; similarly given conditions B. Which conditions are the forever, all time, perfectly correct ones? Neither. Or, that is to say, probably neither. Unless those conditions, A or B, can be deduced (in the rare, technical sense) then it is a subjective choice which of A or B (or C, etc.) to accept as part of the prediction statement.

If I predict that “It’s likely that Mitt Romeny wins the Republication nomination in 2012” then this isn’t a (hard) prediction because the proviso “likely” is ambiguous, and it turns the prediction into a probability. (The event is contingent, meaning it is not necessary true.) We haven’t covered these “soft” predictions yet. For the moment, accept that we have to make the prediction non-probabilistic. Change the prediction to “Mitt Romeny wins the Republication nomination in 2012.” Now, if a week from today Romney finally reveals to the world that, one lonely dark night a decade ago, he was abducted by a UFO and probed assiduously—that is, if Romney has a Ross Perot moment—then, except among a sliver of the electorate, support for the man will plummet and he will lose.

I may then protest that I had not considered otherworldly influence and that it was not reasonable that I should have done so: the prediction is voided. I will convince some of you that this was so, that it was unreasonable to imagine every possible contingency and that given my excuse the prediction is indeed voided. But I won’t convince everybody, and among those recalcitrants—who accept the original prediction as read—my forecast was a bust. Both sides are right, depending on which additional evidence is assumed as belonging to the original conditions.

The conditional nature of predictions is no different than that for logical or probabilistic statements. We know that since “All Martians wear hats & George is a Martian” that “George wears a hat” is true, its probability is 1, the prediction is deduced to be so, even though we know, via other evidence that “No Martians exist.” That is, if we accept the original conditions, George certainly wears a hat, but if we insist that “No Martians exist” then George certainly does not wear a hat. Different sets of conditions give different predictions (or probabilities or truth or falsities or even absurdities).

Next time: the IPCC example.


  1. DAV

    Since we are being persnickity, you said:

    I say that the Detroit Tigers … will beat the Boston Red Sox when they meet on Opening Day, Thursday, 5 April 2012. This is a prediction.

    and later defined beat: score more runs than

    Nowhere did you say anything about “at the end of the game”. Presumably sometime in your 1-1 scenario, the score was 1-0 and the team with the first run “beat” the other team by your definition.

    My point is that some allowance should be made for common understanding. Your point on specificity is well-taken but who wants to read a 20 page prediction written by a lawyer for other lawyers? However if what you are really getting at are weasel words in a prediction (“likely”, “could”, “may”, etc.) which effectively renders the prediction a tautology, I totally agree.

  2. Ken

    All this is just so much philosphizing comingled with being “persnickity” relative to presentation detail…which is fine & well for academic thought exercises but quickly drifts to little relevance for matters in the Real World.

    A good analogy, if not precisely applicable extension of the concepts discussed in ad nauseum detail here is contract law & how the clearly expected outcome, when it actually differs from the clearly expected outcome, is actually handled (or not, depending on one’s perspective) in the Real World. Here’s some real examples, with the most recent case, involving application of pesticide to a residential home going horribly wrong being a very noteworthy example of what really happens out there:

    KALTMAN v. ALL AMERICAN PEST CONTROL INC. Record No. 092541. — March 04, 2011 case decision at: http://caselaw.findlaw.com/va-supreme-court/1557995.html

    Some applicable, legal, definition defining explained at: http://www.vsb.org/docs/valawyermagazine/vl1010-tort-contract.pdf

    “The Economic-Loss and Source-of-Duty Rules and the Wall between Tort and Contract in Virginia,” by Edward E. “Ned” Nicholas III and Sean M. Golden at: http://www.vsb.org/docs/valawyermagazine/vl1010-tort-contract.pdf

    Fraud in Baseball Stadium Example: http://www.thefreelibrary.com/Contracting+for+cooperation+in+recovery.-a0171294327 (Just read the intro paragraph & learn that a contract specifying certain work to be done is in breach–maybe–if that work is not done…however…the fact that the contractor lied about doing the work on completion forms does not constitute “fraud.” — I.E. in actual Real World practice, values are applied that almost immediate render the logic presented in this blog uttlery irrelevant for being out of touch with reality…such as it is.).

    A lawyer blogs about how contracts (definitions of scenarios agreed upon achieving) are actually handled when things go differently: http://www.valanduseconstructionlaw.com/articles/contracts-1/

    Poorly, or not, defined criteria for a bet’s outcome has very very very close parallels to Real World issues associated with defined investment payout allocations, the definition for “job completion,” etc.

    Chances are, if anyone takes the time to read the first legal case decision, above, they/you will be appalled at what constitutes proper legal criteria as actually implemented (the legal concept is “Diminished Economic Expectations”–which correlates directly with the blogger’s ““unexpected turns of events”” jargon; which, is related to another, “Detrimental Reliance.”)

    We’re all better served when such discussions stay linked to the Real World–to ensure they have practical relevancy. Noting things as-they-are is important becuase that’s what counts, not how-things-ought-to-be based on some underlying, and often irrelevant & thus adversely consequential, personal values.

  3. Briggs


    Quite right about common understanding, particularly about common predictions, such as sports contests. We don’t need all this verbiage when agreement is expected. The point will be that scenarios, as opposed to predictions, abuse the privilege (and what are the consequences).


    The difference between predictions and scenarios is entirely “real world.” We can’t just sweep under the rug all necessary qualification just because it happens to be dull.

  4. DAV

    The point will be that scenarios, as opposed to predictions, abuse the privilege (and what are the consequences).

    Couldn’t agree more. My dictionary defines “prediction” as: a foretelling; a prophecy. It defines “scenario” as: a sequence of possible events. Merely stating a possible outcome is hardly equivalent to declaring it will come to pass. Apparently though, many confuse the words. There was some discussion yesterday indicating this.

  5. Prediction is very difficult, especially about the future. Niels Bohr Danish physicist (1885 – 1962) …

    However, predict we must. That is if we are going to achieve successful action. At the very least, it takes many milliseconds for sensory signals to reach our central processor and many more milliseconds to compute our actions in response, and then many more milliseconds to act. By that time, events have moved on to a new state about which we have no information but our computed prediction.

    From that point, the difficulties of prediction compounds. We have even less information about the state of things in the more distant future but we must act in preparation of them. Again, we are computing (predicting (estimating (guessing (winging it)))) what we must do to continue to be successful. It is based upon the expectation that the future will be a computable continuation of the past – not always obtained. All of this is way before we make a bet with someone else about some future event such as some largely irrelevant outcome of a baseball game.

    Life happens and no one gets out of life alive.

  6. Eric Anderson

    “Now, if a week from today Romney finally reveals to the world that, one lonely dark night a decade ago, he was abducted by a UFO and probed assiduously—that is, if Romney has a Ross Perot moment—then, except among a sliver of the electorate, support for the man will plummet and he will lose.”

    LOL! This reminds me of the Frasier episode in which Frasier’s preferred candidate confides to Frasier in utmost confidence that he has been abducted by aliens, and Frasier, in his typical try-to-do-the-right-thing-but-mess-it-up style later spills the beans on public radio.

  7. Eric Anderson

    Briggs, thank you for today’s follow-up post. I believe you have some salient points.

    However, I’m not sure it is the question of adequately defining the provisos that determines the distinction between a prediction and a scenario. It is certainly possible, indeed it is almost certainly the case, that scenarios also carry a whole range of explicit and/or implicit provisos.

    Let’s take the blanket prediction that Romney will win and turn it instead into a series of scenarios of various outcomes of the vote. In one scenario he wins with a 70% vote; in another scenario he wins with a 60% vote; in a third he barely wins by the skin of his teeth. We can come up with any number of possible outcomes and call them scenarios. However, if his alien abduction is revealed it will most certainly cause all of our scenarios to be way off base. Then, should we care to do so, we could argue about whether the scenarios were reasonable.

    The easiest escape clause for the scenario promoter at that stage is to simply state that these weren’t predictions anyway, just scenarios. It may well be true that they were not predictions, just scenarios. But that does not in any way change the fact that the scenarios were conditioned on a bunch of provisos, just as surely as a prediction would have been.

    The difference between predictions and scenarios is not that one has provisos and the other doesn’t. The difference is that in the former we are willing to stick our necks out and say “will” where in the latter we are only willing to say “might”, “could”, “possibly” and so on. It is a question of the level of certainty, not the existence or absence of contingency (provisos).

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