Some years ago I bought �20,000 of premium bonds in separate batches from �500 to �2000. I won a �50 prize nearly every month but hardly any came from the �500 lots but mostly from the �2000 batch. In fact it seemed to prefer one particular batch which came up trumps time and time again. The reason I assumed was that people with similar numbers to mine were cashing theirs in so giving me better odds. The statiticians amongst us will deny this but there was something peculier going on.