A recent visitor asked

"What are the chances of a positive response to a Stayman enquiry ?"

His partnership NEVER bids 1 NT with a five card major, nor with two doubletons!!.

Answer: There are 18 possible hand shapes and 10 contain at least ONE four card major.

Therefore the answer to his question is 55.56%!!

If a 5 card major IS allowed, there are 20 possible hand shapes and 12 now contain at least One four (or 5) card major.

Thus the percentage goes up to 60%!!

Hand Shapes This table shows percentage probability for each hand shape. The last column shows the probability when the suits are specified too.
Pattern % Total % Specific
4,4,3,2 21.5512 1.79600
4,3,3,3 10.5361 2.63400
4,4,4,1 2.9932 0.74800
5,3,3,2 15.5168 1.29300
5,4,3,1 12.9307 0.53900
5,4,2,2 10.5797 0.88200
5,5,2,1 3.1739 0.26400
5,4,4,0 1.2433 0.10400
5,5,3,0 0.8952 0.07500
6,3,2,2 5.6425 0.47000
6,4,2,1 4.7021 0.19600
6,3,3,1 3.4482 0.28700
6,4,3,0 1.3262 0.05500
6,5,1,1 0.7053 0.05900
6,5,2,0 0.6511 0.02700
6,6,1,0 0.0723 0.00600
7,3,2,1 1.8808 0.07800
7,2,2,2 0.5129 0.12800
7,4,1,1 0.3918 0.03300
7,4,2,0 0.3617 0.01500
7,3,3,0 0.2652 0.02200
7,5,1,0 0.1085 0.00500
7,6-0,0 0.0056 0.00050
8,2,2,1 0.1924 0.01600
8,3,1,1 0.1176 0.01000
8,3,2,0 0.1085 0.00500
8,4,1,0 0.0452 0.00200
8,5,0,0 0.0031 0.00030
9,2,1,1 0.0178 0.00100
9,3,1,0 0.0100 0.00040
9,2,2,0 0.0082 0.00070
9,4,0,0 0.0010 0.(4)8
10,2,1,0 0.0011 0.(4)4
10,1,1,1 0.0004 0.00010
10,3,0,0 0.0002 0.00001
11,1,1,0 0.(4)2 0.(5)2
11,2,0,0 0.(4)1 0.(5)1
12,1,0,0 0.(6)3 0.(7)3
 13,0,0,0

  0.(9)6

 0.(9)2