Rituals, surrogate markers, and turf performance outcomes

When a measure serves as a surrogate for the desired outcome, then achieving that measure or endpoint isn’t the real goal

A couple months ago I was struck by this post—“Problems with surrogate markers”—on Andrew Gelman’s blog. “Wow”, I thought, “this seems related to turfgrass management in a lot of ways.”

Wikipedia describes surrogate endpoints, or markers, as:

a measure of effect of a specific treatment that may correlate with a real clinical endpoint but does not necessarily have a guaranteed relationship.

In the Gelman blog, the problem is described in a quote from this article in Health News Review by Mary Chris Jaklevic. This is about human health, but can you notice any parallels with turf maintenance?

“New drug improves bone density by 40%.”

At first glance, this sounds like great news. But there’s a problem: We have no idea if this means the drug also cuts the risk of bone fractures, which is the outcome that we really care about.

The objective of turfgrass maintenance is to produce the desired surface for a particular site. The outcome that we really care about is producing those surfaces. For things to measure, then, it makes sense to either measure those surface conditions, or to measure surrogate markers that are closely and consistently correlated with the surface conditions.

Here are some examples of surrogate markers that are used pretty often in turfgrass management but that are not consistently correlated with the outcome that we really care about:

  • leaf tissue nutrient levels
  • surface area removal/displacement from aerification
  • base cation ratios in soil
  • infiltration rate
  • canopy temperature after syringing

I know some people will disagree strongly with this way of thinking, but I also know I’m not the only one who thinks the surface conditions should be the focus. Some of these measurements, and the maintenance practices associated with them, seem like rituals, rather than necessary work, when one looks at them as surrogate markers for the desired outcome.