Thats the way I used to pick my over / unders. Then I started getting flogged by sportstab and have given up for a while. I found it worked better on the NBL than it did on the NBA.

I also use a similar guide in picking the "Total Goals Scored" in the soccer, (usually over 2.5 or under 2.5).
I add the total goals scored for and against both teams and then divide by the total number of games both teams had already played.

Also used the same logic for NFL games.

Mate if you use it as a guide and test it on all games you get some interesting results. A problem I found was that sports tab would not always offer the option on every game. So I just monitored it myself for a while, without placing any bets. When I thought I had it sorted, I used. It worked well for a while then, as I said earlier sportstab started flogging me. Maybe I started doing something wrong but I abandoned the process anyway.

Occassionally I still use it when the score line is very low or very high, and I think I can get away with it.

So long as it is not the only thing you consider before placing your bet. You also have to look at home and away, injured or rested players, heavy schedules etc.....

It is a tough bet though.

Good luck!