October 12th, 2005, 7:31 pm
Whilst I totally agree with what exotique said, I just thought I would put in my 2 cents worth on calculating the correlation of asynchronous time series.Try using weekly data instead of daily data. With higher frequency data, a larger percentage of the total covariance will be made up of non-overlapping time periods. With weekly data, you will still have the same amount of nonoverlapping data, but as a percentage of the total co-movement of the underlyings it is much less.I first saw this when a colleague was pricing the infamous FTSE-S&P worst-of-2 put spread. If you use daily closing prices, correlation was around 30%. If you used weekly data is was more like 70%! Of course this is more likely to happen with equity index correlation than with an equity index against a currenty pair. But it might be worth having a look. By the way, I suggest using non-overlapping time periods. Do the calc for Monday data, Tuesday data, etc. If you find a wide variation by day of the week this should tell you something about the stability of the correlation figure you produce.For very long dated options (like 10yrs +) it may be important to look at the correlation of the historical forwards, but I expect for short dated options it wouldn't matter.Again pricing has almost nothing to do with historical data anyway, as exotique said.