Pat Haden and Roger Staubach, and Dan Pastorini and Terry Bradshaw face each other today in the NFL playoff games. Which quarterback has the statistical edge?
The NFL QB rating system gives equal weight to a quarterback's completion percentage, average yards per attempt, touchdown and interception percentages.
But when a computer compares these factors to a team's offense, it is found that these factors are not equally important and there are other statistical measures that tell more about quarterback efficiency.
The most important passing stat is yards per attempt. There is a 70 percent correlation between that statistic and a team's offensive performance.
A statistical correlation measures the association between two factors, showing how they vary, or move up and down, together. It can be expressed as a percentage, ranging from zero to 100.
So the 70 percent correlation between yards per pass attempt and team scoring means that it a quarterback is first in the league in yards per attempt, there is a 70 percent chance that his team is first in scoring.
By comparison, the least important stat is the quarterback's interception percentage. Computer analysis shows only a 1 percent correlation this season to points scored. There simply is no statistical relationship between interception percentage and points scorec.
In the vital area of yards per pass attempt, Terry Bradshaw and the Steelers are tops among the four playoff teams, with 6.66 yards per attempt, second in the NFL. The Rams and Pat Haden earned 5.75, last among the playoff teams and 13th in the league.
Today's Pittsburgh - Houston matchup pits the Steeler passing strength against a potential Oiler weakness. Defensively, Houston is allowing 6.1 yards per pass attempt, 23rd in the NFL.
In the Ram-Cowboy game, Haden will be throwing into a Cowboy pass defense that allowed 4.7 yards per pass attempt, second best in the league. Since the Rams rank first with a 4.6 figure, both teams should have to work for the aerial yardage.
Two other stats that measure the passing game but which are not part of the NFL rating system are first down percentage and general passing inefficiency.
The percentage of pass attempts that generate first downs is an important stat, correlating 54 percent with points scored. Bradshaw ranks first in the league with 39.2 percent of all passes going for first downs. Of the four playoff teams, the Rams are the weakest here, ranking 14th with a 31.8 figure.
There are two ways to measure passing efficiency: what you earn each time you go to the air (yards per pass attempt) and what you lose on sacks and interceptions each time you throw.
If you add sack yards lost and interception yardage returned and compare that sum to total yards gained passing, you come up with a passing inefficiency percentage that correlates 28 percent with points scored.
The strongest teams in the league give back about 10 percent of their passing yards in sacks and interception return yardage. Jim Hart of St. Louis was the league leader in both 1976 and '77. Seldom sacked and rarely intercepted, Hart's inefficiency figure was only 10 percent.
By comparison, the weakest teams give back 40 to 50 percent of their aerial yardage. Tampa Bay in 1977 and San Francisco this season are typical of teams with inefficient passing attacks.
This season Dallas and Houston rank first and second in this inefficiency figure, giving back only 11.9 and 12.5 percent of their yardage, respectively.
The weakest of the four teams in this area is again the Rams. Haden gives back 16.2 percent of his air game on sack and interception return yardage. The Cowboy sack pack, which averages 3.6 dumps per game, should cut into his passing efficiency.
These statisties support Bradshaw as the quarterback who operated most efficiently this season.He ranks first among the four playoff quarterbacks in the two most important NFL rating factors -- yards per attempt and percentage of touchdowns per pass -- and is the league leader in first down psssing percentage.
The figures also support the Steelers and Cowboys as favorites in today's games.