[Douglas43]

You are in fourth seat. Left-hand opponent, partner and right-hand opponent all pass. You have a borderline opening bid. Do you bid or do you pass? This hand from a BBO instant tournament is an example of that decision:

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Help is at hand in the form of the "Pearson Count" or "rule of 15". You add up your high card points and your number of spades. If they reach 15 you open, if not, you pass the hand out. In this case you have 12 hcp and only 1 spade, so a Pearson Count of 13, and a definite pass. The rule of 15 works on the principle that when both sides have about the same number of points, the side with the spades can play the hand a level lower than the side without. And where your hand does not meet the rule of 15, it's usually the opponents who have the spades.

In bridge no method is infallible and sometimes you will get a lousy score, but I think I average over 60% by following the rule of 15, which is a good return for doing nothing.
The excellent BridgeBum website (run by Jeff Tang from North America) describes this in more detail: Pearson Points (Rule of 15) - Bridge Hand Evaluation When Bidding (bridgebum.com)
On this hand about 80 out of 373 players passed, and they scored 84%. About 20 made 2♦ for a better score. The remaining 270-odd got a minus score. Actually partner had the spades, but it didn't help much. The full hand:

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[Cyberyeti]

Well W made a pass I wouldn't have made, if he opens I suspect EW go plus

[pescetom]

Playing 2/1 I would not open W, unfortunately.
But then I would have an easy pass as S, rule of 15 or not (I would be tempted to pass it as dealer for that matter).

[mycroft]

Pearson points or not, I have an effective 10 count with little hope our fit is a major, and high chance theirs is the boss suit. What, pray tell, is the upside of opening this, besides getting to play 13 tricks?

If I do open, I lie. I never lie in a major, and this time it will bite me. But the only thing I would think of opening is 1NT that includes 12s. But why?

[Cyberyeti]

pescetom, on 2022-January-24, 09:58, said:

Playing 2/1 I would not open W, unfortunately.
But then I would have an easy pass as S, rule of 15 or not (I would be tempted to pass it as dealer for that matter).

Playing 2/1 the W hand may not quite be an opener, but with those intermediates I rate it as closer to 12 than 11 despite the stiff K. Acol is an easy opener

[Douglas43]

Thanks for those comments. I was focussing on the rule of 15 aspect, but yes, I would open the West hand myself.

[pescetom]

Douglas43, on 2022-January-24, 10:54, said:

Thanks for those comments. I was focussing on the rule of 15 aspect, but yes, I would open the West hand myself.

Maybe take a J from W and give to S, the rule of 15 aspect would be more clear cut IMO (and EW still have 1NT).

[steve2005]

I was one of the people who passed for an 84%.
Didn't like the hand singleton Q♠ not working, and we will likely be out bid with the likely split in hcp

[mikeh]

While I agree that one should pass the south hand, I caution against a robotic application of the rule of 15 (also known as Cansino)

I played a more match years ago against a good pro and client. The client passed out a red two suiter with 12 hcp and a stiff spade. The pro asked to see his hand and was (politely…he’s a good pro) upset because 4H was excellent and easy to get to after a 1H opening. He laughed when he learned that the cards broke badly and 4H failed.

Our teammates reached tge doomed gam3 and we lost the match by 1…we’d have won by 2 had the board been pushed (and by more had th3 good game made)

He told his client that the rule only applied to hands one would think of passing in 1st or 2nd seat.

That’s my advice as well. Don’t use it to make you pass a normal opening bid.

Here, south has a borderline opener, because the diamond suit is weak, the hcp are minimal and the stiff Queen should not be valued as a 2 count. Also, one has an uncomfortable rebid problem looming

[TylerE]

Cyberyeti, on 2022-January-24, 09:25, said:

Well W made a pass I wouldn't have made, if he opens I suspect EW go plus

For that matter with an ok-ish 10 E outta find something to open in 3rd even if W doesn't...

[P_Marlowe]

mikeh, on 2022-January-24, 11:41, said:

While I agree that one should pass the south hand, I caution against a robotic application of the rule of 15 (also known as Cansino)
<snip>
That’s my advice as well. Don’t use it to make you pass a normal opening bid.

Just highlighting.
The part, that the Cansino / Pearson rule is only applicable, if the hand in question is borderline, is quite often ommitted,
making the rule a joke.