THE RESULT
What the data shows
The largest computed metric is 0.9526 for 2004-04; the smallest is 0.8122 for 2005-04. Metric: rho (Spearman correlation).
A changing correlation can reflect pollution range or environmental shifts, not necessarily hardware deterioration.
| month | paired hours | rho | median co | median sensor |
|---|---|---|---|---|
| 2004-03 | 492 | 0.9284 | 2.1 | 1,207 |
| 2004-04 | 468 | 0.9526 | 2 | 1,143 |
| 2004-05 | 592 | 0.9045 | 1.8 | 1,065 |
| 2004-06 | 607 | 0.9123 | 1.8 | 1,031 |
| 2004-07 | 558 | 0.8812 | 1.6 | 1,033 |
| 2004-08 | 428 | 0.8575 | 1.2 | 972 |
| 2004-09 | 555 | 0.9445 | 1.8 | 1,040 |
| 2004-10 | 392 | 0.951 | 2.5 | 1,219 |
| 2004-11 | 679 | 0.9087 | 2.3 | 1,111 |
| 2004-12 | 561 | 0.8789 | 2.3 | 1,081 |
| 2005-01 | 616 | 0.8439 | 1.7 | 1,103 |
| 2005-02 | 588 | 0.863 | 1.65 | 1,043 |
THE METHOD
From source to answer
Monthly paired correlation, coverage and median level comparison.
The Python source exposes this study’s transformations. The complete project download includes shared preparation and evaluation routines.
THE NEXT DECISION
What follows from the finding
Investigate changes in calibration conditions before updating a monitoring model.
Where the conclusion stops
The -200 sentinel is treated as missing. Reference instruments have incomplete coverage; comparisons use paired observations. Sensor calibration is retrospective, not a health or regulatory compliance assessment.
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.