While considering historical spreads I stumbled across this web page with the history of spread betting which I thought was an interesting read.
http://www.financial-spread-betting.com/History-and-risk.html
Sometimes while trying to code strategies in today’s environment it is interesting to consider the bigger picture when trying to understand the relevance of our back test data.
Here is the results of a simple SP500 weekly strategy and the point where data becomes relevant is not hard to spot.

Not much point in testing on any data before spread betting and computers hit the markets!
What I would be interested to know is how spreads have changed over the years. My feeling is that on indices the spreads will most likely have been a percentage of price and increased during volatile times but we have no way of using these varying spreads in our back tests which makes the back test results pretty meaningless. Which I guess is why lengthy forward testing is so important.
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