When Everything Checks Out—and Still Doesn’t Add Up
In the last post, I walked through an example of how selecting for larger ERV can shift the final result—without causing it to fail.
That kind of shift is easy to miss, because everything still looks technically correct.
There are cases where everything checks out.
The test meets criteria.
The results appear valid.
Nothing raises an obvious concern.
And still, something doesn’t add up.
These cases are easy to overlook, because there’s no clear error to point to.
The system is working as designed.
And that’s part of the problem.
What I’ve come to realize is that a result can be technically valid without fully representing what’s actually happening.
Not because of a single mistake—but because of how the test is performed, selected, and interpreted.
The ERV example is just one version of this.
A specific selection choice becomes a pattern.
That pattern shifts the relationship between variables.
And over time, it changes what the result actually reflects.
Not dramatically.
Not enough to fail.
But enough to matter.
I’ve seen this show up across different tests.
Small decisions—how something is performed, which efforts are selected, how a result is framed—can all shape the final output while still staying within acceptable limits.
This isn’t about bad testing.
And it’s not about obvious errors.
It’s about the space where everything looks correct—
but still doesn’t fully explain the patient.
Once you start to notice it, you see it more often.
Not as a failure of the system—
but as a reminder that what gets selected, and what’s actually happening, aren’t always the same thing.