System abandoned

I've decided to abandon my Place Laying System. Further analysis of historical data shows that the system doesn't work at this time of year. This graph shows the average profit (in £s) per race for each calander month. November is the only unprofitable month of the year and December is barely profitable. October does okay, but we're at the end of it and I think the bad times may have begun.

I've lost £200, but I think it's been worth the lesson that I need to check if a system is seasonal. There's probably more that I can learn from this.

Is it just the cold weather?
Is it the change of going?
Is this system mainly for flat and all weather racing?
Is it certain racecources?

Anyways, it looks like a system that should do well from March to October.

I also need to get more data from before Sept 2008 to help provide a clearer picture.