*****SPAM***** [amibroker] Data mining bias vs number of observations

["si00si00" <si00si00@xxxxxxxxx>]

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Hi all,

I have a friend who has developed a trading system. It is an intraday
system that makes on average around 5 futures trades per day. We were
discussing it the other day and a point of disagreement arose between
us. He claims that there is no necessity for him to test the strategy
on out of sample data because he has back tested it using over 8 years
of historical intraday data, and the patterns the strategy predicts
occur 70% of the time or more.

My question is, does anyone know if the data-mining bias can be
considered irrelvant when the sample size is so large? (in this case,
the sample size is roughly 8400 trades). Put another way, with so many
observations, how many different rules would have to be back tested in
order for data-mining bias to creep in?

Thanks in advance for any thoughts you might have!

Simon



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