How PoaIndex Selects NTEP Test Sites

When you enter a ZIP code into PoaIndex, the system does not simply find the

closest NTEP location and ignore everything else.

It uses two kinds of evidence:

local evidence and regional supporting evidence.

That distinction is important.

Why not just use the nearest site?

The closest NTEP test location is geographically relevant, but it may have only

a small amount of usable historical data for a particular grass species.

Another site slightly farther away may contain many years of trials across a

much larger set of cultivars.

Using only the closest site can therefore make a recommendation depend too

heavily on one small experiment.

Ignoring the closest site entirely has the opposite problem: strong local

information can disappear simply because a farther site has more data.

PoaIndex rec-v4-c1 is designed to balance those two concerns.

The local anchor

PoaIndex first looks for the closest NTEP site with enough valid Turfgrass

Quality evidence to make a useful comparison.

That becomes the local anchor.

The role of the local anchor is geographical relevance.

For a ZIP near a nearby university turf testing program, this allows genuinely

local NTEP evidence to contribute even when that location does not have the

longest historical record.

Regional supporting sites

PoaIndex can then add up to two stronger regional supporting sites.

These sites must meet higher longitudinal evidence requirements, including

multiple years of testing and enough cultivars to form a meaningful comparison.

More recent evidence is preferred.

Their purpose is not to override the local site automatically. They provide a

broader historical context around it.

Example: southern New Hampshire

For a location such as ZIP 03062, Amherst, Massachusetts is geographically

much closer than NTEP sites in Connecticut or New Jersey.

Under the current methodology, Amherst can serve as the local anchor while CT1

and NJ1 provide longer-running supporting evidence.

Conceptually:

03062

↓

MA1 — local NTEP evidence

+

CT1 — regional multi-year support

+

NJ1 — regional multi-year support

That is more informative than pretending either geography or dataset size alone

should determine the result.

Distance does not increase a cultivar's score

PoaIndex does not give a cultivar extra performance points just because an

observation came from a geographically closer site.

The site's actual NTEP performance evidence enters the recommendation.

Distance determines which evidence is relevant enough to consider; it is not a

synthetic turf-performance score.

Why multi-year evidence matters

NTEP itself cautions that turfgrass results can vary from year to year and

location to location.

A cultivar that looks exceptional in a single year may be experiencing

unusually favorable conditions.

Repeated performance across several years gives a more stable picture.

That is why PoaIndex reports performance and confidence separately.

A cultivar can have:

high performance with limited evidence, or

high performance with strong multi-year evidence.

Those are not the same claim.

Why PoaIndex shows the sites

A recommendation should be inspectable.

PoaIndex therefore exposes the NTEP evidence locations used to produce the

result instead of hiding them behind a generic "best grass" label.

The goal is not merely to tell you what ranked first.

The goal is to let you understand why.

Next: How to Read NTEP Ratings

Sources

• NTEP interpreting data