Premium Bonds as an investment?

I've been doing some simulations and have some preliminary results. For £30k in ernie, I make it about 16% chance of getting 4% or more back in any 12 months; it seems to be higher if you "invest" less (~26% for £10k; I find this counter-intuitive). The most likely 12-month returns are, respectively, about 3% and 2.5% (i.e. higher if you invest more). There seems to be a ~50% chance of earning 3% or more for any number of bonds over about 3000.

This is using data from the published Dec 2004 prize list, and always assuming I've done my sums (& coding) right of course :-) The answers are very dependant on the quality of the random number generator used.

In message , Mike Scott writes

This is the key.

ERNIE doesn't use a 'computer' type random generator.

Simulations run on PCs and most computers use random number generators arent random.