Bias ?

[Fixit]

In viewing Premium Bond winning numbers it seemed as if more recently purchased bonds stood a far better chance of being selected than mine ...pre 1969...just how many bonds go into the draw each month and is it possible to view statistics to determine bias ...if any?

[pamnez]

We have bought Premium Bonds from as far back as 1959. 5 years ago, I bought a �500 block. I have not won a single penny.  Something wrong somewhere.

 

[Closer]

I've recently bought a fairly large amount of premium bonds, and won �50 in my first month ! I'm told by colleagues that this is fairly common as they have all won shortly after buying more bonds.