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The table is from Thomas's Bridge Fantasia Many unique information related to statistical analysis of bridge hands including Law of total tricks and hand evaluations.

How often does a double-double fit occur when the total trumps is n, for n=14...23? 

Total trumps % with DDFits
14 0.0%
15 0.0%
16 11.9%
17 0.0%
18 28.3%
19 10.8%
20 25.2%
21 17.5%
22 27.4%
23 12.9%

More often for even number then odd number.

This information combined with how often each number of total trumps occur give you even better judgment on what you should bid base on statistical distribution of the bridge hands.