COBRA Evaluation

This HTML file was created from a pdf file so that
we could add comments and link it to the entries
in the HandVal table of CardShark BidBase.
The links and comments are in brackets and in red.
The non-red material in this file was written by
Torbjörn Lindelöf, the creator of COBRA

The value of a hand, i.e. its trick winning capacity, depends mainly on its high-card strength and on the lengths of its suits, but also, to a certain extent, on the location of the honours. In fact, honours located in long suits are usually more valuable than honours accompanied only by few cards. Furthermore, honour strength held to the left of an opponent with some high-card strength is generally more useful than the same honour strength to the right of the strong hand.

More generally, the value of one hand depends on the complete distribution of all four hands. Hand evaluation in the COBRA system therefore proceeds with the bidding to convert information about suit distribution and honour location into points that will be added to or subtracted from the playing strength of the hand.

Section 3.2 describes the COBRA Basic Point Count (BPC) or the point count of a hand immediately after the deal and before the auction has started. Section 3.3 describes modifications to the BPC as more information about the other hands is obtained.

The COBRA point count is so adjusted that a JPS of 28 PP ["JPS" and "PP" are not defined in this document, but PP is simply Playing Points, which are the total valuation points detailed herein, while JPS appears to be total PP for one side as indicated by the bidding.] gives the partnership a better than 50% chance of making 10 tricks in their best trump suit. Any additional trick requires another 3 PP.

The COBRA BPC is almost independent of the COBRA bidding system as such and COBRA hand evaluation is (almost) system independent. COBRA hand evaluation was used in computer experiments with other (already existing) bidding systems before work on the COBRA bidding system had even started, in order to improve the precision and accuracy in their description. COBRA hand evaluation improved the precision in the sense that words such as ‘approximately’, ‘about’, etc., could be removed from the bidding rules. The higher accuracy meant that the relationship between combined point counts for partnership hands and their trick-winning ability became a much closer one than in most previously published evaluation systems. These statements are based on several million hands which were analyzed to define the COBRA BPC.

A consequence of the independence of the COBRA point count method from COBRA bidding is that the former can be used advantageously, almost without adjustment, to enhance the precision of most other bidding systems.

3.2 The COBRA basic hand evaluation

The basic point count (BPC) is a measure of the probable trick winning power of a hand, given no information about the other hands. It is directly used by the dealer when he considers an opening bid, and is otherwise used as a basis for evaluating the point count at any time during the auction.

The BPC is evaluated as follows:

a. High cards

  1. Evaluate the honour strength.

    [C1010-C1020 -- The .25 additional for the Ace and the .25 for the Ten are from c.1 and k.4, below.]

b. Distribution
  1. Add 1 PP for each biddable suit.

    [Lindelöf defines a biddable suit as any 5-card suit (C1120) or a 4-card suit with either 3 honors or 4+ HCPs (C1110} The only 3-honor holding which would be less than 4 HCPs is QJT. Any honor sequence starting with A, KQ, or KJ will always be 4+, so we don't have to show sequences which build on those (e.g.: KQJ).

    In C1120, a suit may have the same honors as in C1110, but since they are not required with 5+ cards, we don't show them.

    The "-E" in the "Suit" field is from h.4, below, which says not to count these points if either opponent has bid the suit.]

  2. Add another 1 PP if the suit is also rebiddable.

    [C1130-C1140 -- A suit is rebiddable if you could take away the 2 smallest cards and it would still be biddable. These definitions of biddable and rebiddable are for evaluation purposes, and do not imply that only such suits may be bid or rebid.

    KJ-sixth (KJxxxx) is rebiddable. It would not pass C1110, which specifies exactly 4 cards, but it would pass C1120. It would not pass C1140 because it is less than 7 cards, but because it has 4+ HCPs and 6 cards, it would pass C1130.

    K-seventh is not rebiddable. It passes C1110 as biddable, but it would not pass C1140 as rebiddable because it is too short, nor would it pass C1130 because it is less than 4 HCPs. Add another 'x' and it would be rebiddable under entry C1140.]

  3. Add another 2 PP if the suit is also twice rebiddable.

    [C1150-C1160 -- KQJTxxxx is a twice rebiddable 8-card suit (C1150) in that you can take 4 cards from it and it will still be biddable. Note that these points are cumulative. This hand gets a point from C1120, another from C1140, and 2 from C1150.]

  4. Add another 3 PP for each card beyond twice rebiddability.

    [C1165-C1170 -- A twice rebiddable suit with 4+ HCPs (or QJT) and 10 cards gets 3 points for each card over 8, but that hand would also meet C1170's specs, which would over-upgrade it, so a Flag is used to prevent both entries from being counted for the same hand.]

c. Controls and shape
  1. Add 1/4 PP for each ace or ten. [C1010 and 1040]
  2. Subtract 1 PP for a hand containing no aces. [C1080]
  3. Subtract 1 PP if the hand contains no biddable suit. [C1180]
  4. Add 1/2 PP for the combination AQJ in any suit. [C1090]
d. Unprotected honours
  1. Subtract 1 PP for any singleton A, K, Q or J. [C1060]
  2. Subtract 1 PP for any doubleton AJ, KJ or QJ. [C1070]

The BPC is independent of vulnerability. Points are not given for the possession of short suits, because it is impossible to tell whether this will be useful or not before anything is known about the other hands. Shortness in a suit is a disadvantage if partner has high cards in that suit, and an advantage if he has losers in the suit. It is true that counting points for short suits often gives approximately the same result as when points are given for long suits, but very unbalanced hands are grossly undervalued by the former method and, furthermore, the short suit point count often requires more revaluation as the auction progresses.

The BPC is designed so that an opening bid generally promises 13+ PP, except for opening bids by P3.

3.3 COBRA hand evaluation based on the auction

Information obtained from the auction is used in order to modify the Distributional Point Count (DPC) so that the resulting evaluation reflects the actual playing strength of a hand in relation to the other three hands.

The three circumstances that may be disclosed by the bidding and which influence the expected trick-winning ability of a hand, are:

  • Usefulness or disadvantage of suit shortness;
  • Establishment of a fit with partner or with the opponents;
  • Favourable or unfavourable position of high cards.
These considerations influence the DPC as follows:

e. Suit shortness

  1. When an opponent shows biddable strength in a suit ‘s’ for the first time; add 3 PP for a void, 2 PP for a singleton and 1 PP for a doubleton in ‘s’.

    [C1190-1210 -- Cobra does not give points for short suits until someone else has bid, as described under 'd', above. The 'E' in the Suit field means Either opponent's suit.]

  2. When opponents confirm a fit in a suit, or
    an opponent shows rebiddable strength in a suit, or
    partner makes a minor suit trial bid in a suit;
    add 2 PP for a void and 1 PP for a singleton in the suit. [C1220-1230 for opponents, C1240-1250 for pard.]

    Note that an opponent may show rebiddable, hence biddable, strength in a suit for the first time in one single bid [such as a Weak-2 opening] - if so, e1 and e2 may apply simultaneously.) [In BB, a hand which meets C1220-1230's specs will also meet C1200-1210's specs and get both set of points.]

  3. If partner shows biddable strength in a suit ‘s’ where less than 2 cards are held; subtract 2 PP for a void and 1 PP for a singleton in ‘s’. [C1260-1270]

  4. If partner makes a mild slam invitation in a suit; or if the JPS is 34+ after a fit has been established; subtract 3 PP having a non-skew hand. [A "mild slam invitation" is too vague for us to quantify. We leave that for better minds than ours.]

f. Fit with partner

  1. Add 1(2) PP for holding 1(2+) honour(s) which is (are) not part of a solid top sequence* in any suit bid or supported** by partner.

    [C1280-1320 -- This is fairly complicated:

    • '? & -A' -- any single honor except A = 1 point
    • 'AKQT' -- the T in this sequence = 1 point
    • 'A? & -K' -- AQ, AJ, AT = 1 point for the lower honor
    • 'AK? & -Q' -- AKJ, AKT
    • 'KQJT' -- 4 honors, but limited to 2 points
    • 'AQJT' -- 3 honors = 2 points
    • 'AKJT' -- the J and the T = 2 points
    • 'AQJ, AQT, AJT' -- 2 lower honors = 2 points ]

    * A solid top sequence is a sequence of touching honours, including the ace, in one and the same suit; i.e. A, AK, AKQ, AKQJ or AKQJT.

    ** A suit where partner indicates a holding which is either biddable or at least constitutes basic support for whatever cards are held in that suit. Thus f1 would not apply to a biddable holding in diamonds when partner opens 1D (which promises no more than a 3-card suit); however, f1 would apply in the same situation to rebiddable diamonds.

  2. The first time a fit becomes established in a hand (in suit 's'):
    • Add 1/2 PP for every ace and 1/2 PP for the ten of ‘s’; [C1330-1340]

    • Subtract 1/2 PP for any Q or non-singleton J outside ‘s’. [C1350-1360]

    • Add the DELTA-value with respect to the shortest suit (by the first player in whose hand the fit in that suit becomes established only).

      [C1370 -- DELTA-value means you subtract the shortest suit from the fit suit. A fit becomes established when partner has bid a suit and you have support for it. It becomes confirmed after you show support for partner's suit, directly (raising) or indirectly (Jacoby 2NT, Splinter, cue bid, Ace-asking, etc.)]

      Note that points for f2 are calculated once only in any one hand, even if another fit becomes established later during the auction. Note also that a fit in a particular suit cannot become established for the first time more than once! Consequently it is not possible for both partners to apply f2 to one and the same suit.

  3. If partner makes a minor suit game trial bid; add 1 PP if biddable strength, including 1 HT [Honor Trick or Quick Trick], is held in that suit.

    [C1380 -- A-any, KQ-any, KJT (per Lindelöf)]

  4. Add 1 PP for the king in a suit where partner has shown the ace.

    [1390C1390 -- The Suit spec of "PCA" stands for "Partner Cuebid Ace".]

g. Position of honours in an adverse suit

  1. Add 1 PP holding a guarded K or Q (or both) which is not part of a solid top sequence in a suit where RHO shows strength.

    [In C1400, 'K' without the leading asterisk means K is the highest honor - no A - while the '& -Q' means no Q. In C1410, '*Q & -AK' means Q is not the highest honor, so you can have AQ or KQ, but not AKQ.]

    An opponent can show strength in a particular suit 's' either by bidding or supporting 's', by making a penalty double of a contract in 's', by bidding a strong 1NT (opening bid or overcall), or by employing an unusual NT-bid.

  2. Subtract 1 PP holding a guarded K or Q (or both) which is not part of a solid top sequence in a suit where LHO shows strength. [C1420-1430]

  3. Subtract 1 PP for any unguarded, but at least doubleton Q or J in any suit where [either] opponent shows biddable strength (except J doubleton with a K or an A).

    [C1440-1450 -- Note that in C1440, 'J' without the leading asterisk means "J and no higher", since AJ and KJ are excluded by this rule and QJ will be caught by the Q test. C1450 covers J-third, which is still considered unguarded.]

h. Fit with the opponents

  1. If partner makes a cue-bid in a suit ‘s’ in which either opponent has biddable strength, showing first- and second-round control in ‘s’; subtract 1 PP for any A, K, Q or non-singleton J in ‘s’.

    [C1460 -- We assume the cue-bid shows shortness, since if it were showing A/K controls, why would we be discounting honors in our own hand? "PSE" stands for Partner Short in Either opponent's suit.]

  2. If, additionally, the partnership has confirmed a fit; add 2(4) PP holding 3(4+) cards in the adverse suit. [C1470-1480]

  3. If partner shows skewness with respect to a suit ‘s’ except as under h1:
    • Subtract 1 PP holding the K of ‘s’; [C1490 -- "PS-E" means Partner Short except in Either opponent's suit.]

    • If the partnership has confirmed a fit; add 2(4) PP when holding 3(4+) cards below a solid top sequence in ‘s’. [C1500-1510 -- "Solid top sequence" is not clearly defined in Lindelöf's files, but we will assume AKQ for this rule. It's possible that the J and even the T should also be included, but that's an awfully long (and rare) side suit.]

  4. If either opponent is found to have biddable strength in a suit where biddable strength is held; subtract all basic PP given for that suit under section b. [C1110-1120 -- The "-E" suit spec means not Either opponent's suit(s).]

i. Positional considerations

  1. P2 subtracts 1/2 PP if P1 passes initially; P2, P3 and P4 add 1/2 PP if their RHO opens the bidding. [C1520-1530]

  2. P3 adds 1 PP for holding biddable spades if P1 and P2 both pass initially.

    [C1540-1550 -- Two entries are needed to show biddable spades, just like the Biddable Suit bonus in C1110-1120. It seems odd that this bonus is just for seat 3, since it is well known that 4th seat should not open with a marginal hand unless he has spades covered.]

  3. Holding rebiddable spades P2, P3 and P4 add 1/2 PP if their RHO opens the bidding with anything but a (natural) spade bid.

    [C1560-1570 -- Again, it takes two entries to show the rebiddable spades. The Position spec of "2-4R-S" means seats 2-4, RHO opened, but not in Spades. We hate to use such cryptic codes, but what else can we do?]

j. Rounding

COBRA bidding rules always refer to integral point count values. The current point count is therefore rounded before it is used. Fractional values are retained throughout the auction, however, because later (fractional) modifications may combine with previous fractional values to make unit changes in the current point count. The following rule thus applies temporarily - it does not permanently change the current point count.

Round to nearest integer value -- down for 1/2.

k. NT-adjusted HCP

The HCP does not change during the auction, but for the purpose of bidding a natural NT a player adjusts his HCP temporarily as follows:

  1. Subtract 1/2 point with no suit longer than 4 cards. [C1590]

  2. Subtract 1/2 point for any 2- or 3-card suit which consists entirely of honours above a ten. [C1600-1610]

  3. Add 1/4 point for each high-card point in any 5-card suit with 2+ honours.

    [C1620 -- It's not clear if "2+ honours" includes the Ten, although every other Cobra reference to honors includes the Ten. Although the Ten does not have HCPs, if the holding is ATxxx, the Ace would get 1 point while if the Ten is not counted as an honor, the Ace would not get the bonus point.]

  4. Add 1/4 point for any ace or ten.

    [This was done in C1010 and C1040. Note that all entries but those are marked as either Suit or NT; C1010-1040 count in both totals.]