I made and publish this index, and I’d like people to pick holes in the method—especially the retailer weighting, missing pack sizes and week-to-week chaining.

The UK Online Shelf-Price Index tracks posted online shelf prices at Tesco, Sainsbury’s, Asda and Aldi. I match the same products between weeks and, for each retailer and broad product class, calculate a Jevons index: the geometric mean of the matched products’ price ratios. Then I chain the weekly changes. Each retailer gets equal weight.

W43, published Monday 26 October, is 99.9645 (rounded to 100.0 on the page), down 0.04% on the week. Almost all of the move came from Aldi, which gets a quarter of the weight; the other three together contributed about 0.001 index points.

The new series starts at W42 = 100. W41 was skipped because collection didn’t complete, so four-week changes are blank until W46.

The full CSV and JSON series are free under CC BY 4.0. They contain index numbers and counts, not product-level prices.…