Below I present a table of the values of ASX (FTSE All Share Index):
21-Sep-2011 2128 (lowest point)
The index dropped 22.5% from the start of the year to 14 September. If you had bought at that point, then by the end of the year, you would have made 11.9% profit; whilst the index returned -13.3% (negative) over the year as a whole. If you had been especially prescient - and there's no real indication that you would have been - and bought at the lowest point, then the index would have dropped 28.5% in the period from the start of the year to 21-Sep-2011, and subsequently gained 21.2% to year-end.
I do not have a value for ASX at 11-Sep-2011, so I need to use the one for 14-Sep-2011. During the decade since then, the ASX has returned an average compound rate of 1.6% pa, excluding dividends. If you had bought at the year-end, then the comparable return would have been approximately 0.5% pa.