Here’s a chart showing how Avatar and Titanic are faring at the box office on a “Same Number of Days In Release” basis, unadjusted for inflation, after four full weeks in release:
The “Avatar %” calculation refers to Avatar’s weekly gross as a percentage of Titanic’s. I.e. if they had the same gross, this would be 100%. This shows a slight weakening of Avatar’s trend in the 4th week, which is pretty much expected since this is the point where Titanic began to completely defy the normal trends. Avatar is defying the normal trends — just not quite as much as Titanic. But then it has built up a huge lead so it doesn’t have to have quite the legs that Titanic does.
And here’s a graph showing the same info: (click to enlarge)