How effective is pair-programming?

Researchers have found that

1. Performance of a pair of programmers is better than the second best member of the nominal group.  
2. Pairs made up of one programmer from above median and one from below the median will ensure high quality software.  
3. Pair-programming leads to increased programmer satisfaction and may result in smaller programmer turnover.
   
4. Pair programming leads to better grades in college courses, and students are more likely to continue their CS or MIS program.  

References: 

1. "ARE TWO HEADS BETTER THAN ONE FOR SOFTWARE DEVELOPMENT? THE PRODUCTIVITY PARADOX OF PAIR PROGRAMMING? by "Balijepally, VenuGopal; Mahapatra, RadhaKanta; Nerur, Sridhar; Price, Kenneth H.. MIS Quarterly, Mar2009, Vol. 33 Issue 1, p91-118, 
   
2. "Are Two Heads Better than One? On the Effectiveness of Pair Programming" by  Dyba, T.   Arisholm, E.   Sjoberg, D.I.K.   Hannay, J.E.   Shull, F.  Simula Res. Lab. Sintef ICI, Bucharest; IEEE Software Nov.-Dec. 2007, Volume: 24,  Issue: 6 pp 12-15
3. "Pair programming productivity: Novice–novice vs. expert–expert KM Lui, KCC Chan - International Journal of Human-computer studies, 2006 
4. Debunking the nerd sterotype