THE RESULT
What the data shows
The largest computed metric is 5.489 for (28.0, 90.0]; the smallest is 3.128 for (0.0, 7.0]. Metric: mae (MPa MAE).
Small holdout groups make age-specific averages unstable; this is a diagnostic, not a new independent test.
| band | test samples | mae |
|---|---|---|
| (0.0, 7.0] | 47 | 3.128 |
| (28.0, 90.0] | 27 | 5.489 |
| (7.0, 28.0] | 95 | 4.501 |
| (90.0, inf] | 25 | 4.775 |
THE METHOD
From source to answer
Stratify grouped-holdout residuals by prespecified curing-age bands.
The Python source exposes this study’s transformations. The complete project download includes shared preparation and evaluation routines.
EVALUATION
How the result was checked
Fixed 80/20 split of unique input groups (seed 42); exact input duplicates stay together.
Fixed configurations specified before scoring; no tuning on the holdout.
Target and input features
Target: strength
Inputs: cement, slag, fly_ash, water, superplasticizer, coarse_aggregate, fine_aggregate, age
THE NEXT DECISION
What follows from the finding
Review error patterns across testing ages when specifying an external validation study.
Where the conclusion stops
Laboratory observations do not certify a construction mix. Composition and curing conditions are confounded. Models require independent engineering validation and cannot replace strength testing.
Related studies may reuse observations or holdouts. These are historical analyses; associations and backtests do not demonstrate commercial impact. Further model tuning needs new, untouched evaluation data.