WIG is 20%+ up YTD... mostly thanks to overnight gaps

The end of the year is near.

In the previous (nearly) 24 months, the broadest index of the Warsaw Stock Exchange - WIG - has gained more than 20%:

Fig. WIG performance YTD till 2012-12-21; source: stooq.com

This noticeable result has been generated thanks to a pretty small positive drift in daily returns - less than 0.1%:

Fig. WIG daily returns in 2012

But what's more interesting, a major part of this year's growth is a result of overnight WIG changes - i.e. gaps between previous day close and the following day's open:

Fig. WIG open-close and close-close daily returns

Meanwhile, while the 20%+ WIG's return is quite impressive, it is quite distant from the theoretical maximum gain possible to be realized with perfect prior knowledge.

Fig. Maximum theoretical WIG gain at 1H frequency.