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Grocery price methodology: fixed 15-item basket
How Grocery Prices Australia is built. Transparency is the point: every product match and price is in the downloadable CSV.
Why the basket never changes
We keep the same 15 staple items in the basket every month. That makes the trend like-for-like: a change in the total reflects price movement in the same basket, not a change in what we are measuring. CHOICE changes its basket each quarter, so it cannot show a continuous trend. We never change ours, so we can.
The basket
We compare the cheapest like-for-like product at each store, which means each store's own brand (home brand) where one exists. That is what a value shopper actually buys, and it is the only fair way to include Aldi, which is almost entirely own brand.
| Item | Pack | Cadence |
|---|---|---|
| Cavendish bananas | 1kg | weekly + monthly |
| Beef mince 3 star | 500g | weekly + monthly |
| Brown onions | 1kg | monthly |
| Salted butter | 250g | weekly + monthly |
| Chicken breast fillets | ~1kg | weekly + monthly |
| Free range eggs | 12pk | weekly + monthly |
| Full cream milk | 2L | weekly + monthly |
| Dry spaghetti | 500g | monthly |
| Brushed potatoes | 2kg | monthly |
| Tasty cheese block | 500g | monthly |
| Black tea bags | 100pk | monthly |
| Diced tinned tomatoes | 400g | monthly |
| Wheat biscuits own-brand | 1.12kg | monthly |
| White sandwich bread | 650g | weekly + monthly |
| Long grain white rice | 1kg | monthly |
Where the prices come from
Prices are recorded from each retailer's own website on the capture date. We log the matched product, its shelf price, the pack size and the date for every point, and flag specials. IGA stores are independently owned, so we price one representative store, Romeo's Food Hall, Summer Hill; another IGA can differ.
Pack sizes and unit price
We match the closest like-for-like pack, then compare the ticket price. Where a store only sells a different pack (for example a 1.12kg box instead of a 575g one), we record the pack we actually priced, so the pack column always matches the product, and you can read the unit price yourself.
Missing matches
A retailer is only included in the full-basket ranking when all 15 items are matched for that capture. If a store has fewer than 15 matched items, its partial subtotal is shown separately and labelled, and it is held out of the cheapest ranking and the trend line so every comparison stays like-for-like.
Out of stock
If a product is temporarily unavailable online, we record the closest equivalent of the same size and brand tier and note it, rather than leaving a gap that would distort the basket.
Cadence
The full basket is captured monthly. A seven-item pulse (milk, bread, eggs, butter, mince, chicken, bananas) is captured weekly for a faster read on movement.
Honest limits
Prices change between captures and with weekly specials, so each figure is a point-in-time snapshot. Own-brand products are not identical between stores, so small differences in size or recipe exist; we choose the closest like-for-like. This is an independent project and is not affiliated with any supermarket.
Corrections
If a product match or price looks wrong, email admin@refdat.com with the retailer, item and capture date. Corrections are applied at the next build.