78 percent of the midair collisions that occurred around the traffic pattern happened at nontowered airports.
This is from an AOPA report which is higher than the earlier study I googled. It does not refer to OH joins but surely any join which involves the honeybee effect of joining at a specific point in the OH plus up to 6 needless 90 degree turns mixing high and low wing aircraft MUST indicate a higher collision risk
On the reverse side of the coin it must mean that any joining procedure which does not involve the honeybee effect and minimises the number of blind 90 degree turns of high and low wing aircraft must lower the collision chance
Pace