With nobody vulnerable at matchpoints, partner dealt and pre-empted three spades with KQJxxxx (and some side values). With three small trumps, I raised him to four, following the Law of Total Tricks, which says that the number of tricks you contract for should equal the total number of trumps. We went down one which got us a bottom, but we would have gotten an above average score if I had passed, allowing us to make 3 spades.
Upon re-examining my holding, ♠ 832 ♡ AQJ7 ♢J75 ♣ kJ5, I came to the conclusion that raising was a bad idea. One reason was the flatness of my hand, the 3-4-3-3 distribution reduced the chances of our opponents also having ten, or at least nine trumps for a total of 19-20 between the two teams. Perhaps more important was the fact that my strong heart holding had "crippled" the suit for the opponents, making it unlikely that they could make four hearts even if they bid it over three spades.
Was I wrong to raise? And if so, was it because I was too strong? Would it have made more sense to raise with fewer points and a more shapely hand? Or is using the law of total tricks out of place in this situation?