Here's a table that shows the distribution of NCAA Tournament at large selections from 2013 to the present:
In the table, the Average ARPI Rank for At Larges column shows the average ARPI rank of each conference for 2013 through 2018. Thus the conferences are arranged in the table in order of average ARPI strength over that period.
Over the entire period, there's a pretty clear dividing line between the Power 5 conferences at the top and the other conferences. Here's a table that puts the Power 5 conferences together as a group and all the other conferences together:
2015 notwithstanding, the table seems to indicate a trend towards increased numbers of at large selections for the Power 5 conferences and decreased numbers for everyone else.
Looking at this from a statistical trend (straight line trend) perspective, here's what the table shows:
As the chart shows, there indeed is a trend towards more Power 5 at large selections and fewer from other conferences. Indeed, if the trend continues, in four years we can expect the Power 5 conferences to get all of the at large selections.
What underlies this trend? A starting point is conferences' average ARPIs. The following table and chart show the trends in the top 10 conferences' ARPIs. These conferences account for all but 3 of the at large selections since 2013.
On the chart, the top 5 trend lines are for the Power 5 conferences. Their average ARPIs all are well above those of the next 5 conferences. And, except for the Big 10, their average ARPIs are trending upward. For the next 5 conferences, their average ARPIs are either stable or trending downwards.
But, what underlies these average ARPI trends? By far the most important factor is the conferences' overall winning percentages in non-conference games. As I've shown in previous posts, these winning percentages are critical, under the RPI formula, in distinguishing the conferences from each other.
The following table and chart show the conferences' overall winning percentage trends:
Once again, the top 5 trend lines are for the Power 5 conferences. As these lines show, for 3 of the Power 5 conferences, their winning percentages are trending higher. The ACC has experienced a slight decline, but only from a high starting position. Only the Big 10 is trending seriously lower.
On the other hand, all of the next 5 conferences' winning percentages are trending lower, except for the stable West Coast Conference.
What does this mean? Unless the trends in teams' ARPIs change, the trend towards more Power 5 and fewer other conference at large selections is going to continue. Indeed, in a few more years, the Power 5 conferences will be getting virtually all of the at large selections. And, the driving factor underlying this is the conferences' winning percentages in non-conference games trends. To be blunt but straightforward, unless something changes in those trends, the Power 5 monopolization of at large selections seems inevitable.
