Price index methodology
The index is a Nositel-specific comparison aid, not an official cost-of-living index.
What is compared
We compare the same canonical product between retailers using the latest valid observed branch price. One branch cannot outweigh another retailer for the same product.
Window and minimum evidence
The current snapshot uses observations from the last 30 days. A category needs at least 3 comparable products; the overall index needs at least 10 comparable products across at least 3 categories.
Calculation
For each product we compare the retailer median with the median price at other retailers. Categories have equal weight, and medians reduce the influence of one-off extremes.
Scale
Below 85% of market is “Very cheap”, 85-95% “Cheap”, 95-99% “Below average”, 99-101% “Average”, 101-110% “Above average”, 110-120% “Expensive”, and above 120% “Very expensive”. Insufficient evidence is shown as “Insufficient data”.
Price comparison across chains
The chain comparison uses a basket of everyday product categories (e.g. “fresh milk”, “shampoo”), not identical items. Prices are normalized per kg, litre, or piece; for some goods (medicines, cigarettes, tea) the price per package is compared.
For each chain we compute the typical price (median) and the price of cheaper options (25th percentile) from its observations. Only chains with current data and enough stores are ranked, and extreme outliers are excluded. Travel retail (airports, roadside) is excluded by default.