Nothing Improved Except the Average

A Kitagawa Decomposition of a Plumbing Franchise Network's First-Visit Resolution Rate Across 486,312 Residential Jobs, Nine Job Categories and Fourteen Quarters

A paper from the School of Continuous Improvement decomposes the first-visit resolution rate a national plumbing and drainage franchise network publishes for each of its territories, using 486,312 completed residential jobs from 214 territories and 4,918 technicians across the fourteen quarters from 2023 Q1 to 2026 Q2. The published rate rises from 71.4 to 76.2 per cent while falling in all nine of the network's own job categories, by between 0.9 and 6.8 percentage points; a symmetric components-of-a-difference decomposition apportions 8.6 percentage points to the composition of dispatched work and minus 3.7 points to category-specific performance. The composition shift dates from an online booking triage introduced in the fifth quarter, which lifted the combined share of tap-and-washer and toilet-and-cistern jobs from 18.5 to 42.4 per cent. Technicians in the top quartile of complex-job share carry a published rate 9.4 points below the network mean, and the dispatch rule allocates complex work by published rate. Twenty-four alternative specifications move the composition component by no more than 0.6 percentage points.

@misc{slop_p1t27w,
  author       = {Bram Ntuli and Fenna Okoro and Petra Umbile},
  title        = {Nothing Improved Except the Average: A Kitagawa Decomposition of a Plumbing Franchise Network's First-Visit Resolution Rate Across 486,312 Residential Jobs, Nine Job Categories and Fourteen Quarters},
  year         = {2026},
  publisher    = {Slop University},
  doi          = {10.5555/slop.p1t27w},
  url          = {https://slop.university/outputs/slop-paper-the-dripping-tap-p1t27w/},
  version      = {1.0},
  note         = {Research paper},
}