# 037. Curing age and measured strength

**Question:** How do strength distributions differ across curing-age bands?

## Result

The largest computed metric is 51.72 for (28.0, 56.0]; the smallest is 18.52 for (0.0, 7.0]. Metric: median_strength (MPa).

Mix compositions differ across ages; this is not a longitudinal estimate of strength gain.

![Curing age and measured strength](outputs/chart.png)

| age_band | samples | median_strength | p25 | p75 |
| --- | --- | --- | --- | --- |
| (0.0, 7.0] | 262 | 18.52 | 12.66 | 30.24 |
| (14.0, 28.0] | 425 | 33.76 | 26.23 | 44.39 |
| (28.0, 56.0] | 91 | 51.72 | 39.43 | 62.69 |
| (56.0, 90.0] | 54 | 39.68 | 32.97 | 47.77 |
| (7.0, 14.0] | 62 | 26.54 | 22.37 | 33.62 |
| (90.0, inf] | 136 | 47.34 | 40.52 | 56.53 |

The chart shows 6 of 6 result rows; the table previews the first 6 in the analysis-defined order. [Download the full result table](outputs/results.csv). Numerical values are computed from the source; missing results stay unavailable.

## Method

Prespecified age bands with median, quartiles and sample counts.

The study uses shared source preparation and reusable statistical routines. Its specific transformations are in [analysis.py](analysis.py), and common model/evaluation code is in [portfolio/methods.py](../../portfolio/methods.py). The [notebook](analysis.ipynb) executes the study and displays the saved results.

## Decision and limitations

Form a controlled curing-time experiment with comparable mix formulations.

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 share observations or holdouts. These are focused analytical studies, not independent replications or deployed business systems. Any model refinements informed by these results need new untouched evaluation data. No commercial impact is inferred from an association or backtest.

## Reproduce

From the repository root, after installing `requirements.txt`:

```powershell
python projects/037-curing-age-and-measured-strength/analysis.py
```

Source data are downloaded automatically if absent. Original archives are retained unchanged and checked by SHA-256. The cleaned cache normalizes column names; field-specific changes are visible in [data preparation](../../portfolio/data.py). Runtime evidence is in [receipt.json](outputs/receipt.json).

## Source

[Concrete Compressive Strength](https://archive.ics.uci.edu/dataset/165/concrete+compressive+strength), Yeh (1998). [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/). Source data are transformed and aggregated in this study. [Source provenance](../../data/provenance/concrete.json) and [prepared-data audit](../../data/provenance/concrete_prepared.json) record the downloaded files, field coverage and hashes.