If partner has not bid, doubles are for takeout— whatever the level. You would double an opening bid of 1♠, 2♠ (weak), 3♠ and 4♠ with, say, ♠4, ♥AKJ7, ♦KJ532, ♣AQ4. The higher the level, the better the hand you’d want for the take-out double. But not by much. The real difference in strategy occurs across the table.

You’d almost never convert a double 1♠ into penalties by passing. You’d need enormous spades eg ♠KQ10982.

The double of a (weak) 2♠ opener will only very rarely be left in. You’d need very good spades eg ♠KQ1092.

The double of a 3♠ opener can be left in rather more. It’s a risky course of action but you might chance it if stuck for alternatives holding, say, ♠J1082.

The double of a 4♠ opener, still ostensibly for take-out, should be left in far more. Almost all balanced hands should pass, for surely four tricks on defence will be easier than 11 on offence.

Computer analyses suggest passing these high-level doubles and converting the take-out to penalties is a long-term winner.