Data notes

How we correct mistakes

We collect prices automatically from the information the supermarkets publish online. Sometimes a supermarket's site changes or fails, and sometimes our own code reads a page wrongly. When that happens:

• We fix the cause, then repair the records it affected, and keep a backup of what we changed.
• We list every repair that touched more than 100 price records on this page, with the dates affected, what was wrong and what we did; for repairs before October 2026, as far as our repair notes go.
• Records we filled in or estimated, rather than collected, are listed on this page with their dates. Our data and charts do not yet mark them, so leave those dates out of any analysis that needs collected prices.
• If a repair changes a figure we published in an article, we add a dated correction note to that article saying what changed. Weekly Briefing editions are kept as they were first generated; the repairs listed here give the dates each one covers. We do not quietly edit published figures.
• Anyone can report a mistake to info@basketwatchireland.com. We reply within 5 working days.

Data notes

• SuperValu, 24 to 27 July 2026: filled days. SuperValu's website did not return thousands of products on these four days. To avoid a false dip in the record, we filled about 11,230 missing product-days with the price we collected on 31 July 2026. These are not prices collected on those days.

• SuperValu Real Rewards, mid-July to 18 October 2026: member prices recorded as shelf prices. SuperValu reworded its Real Rewards labels in July and our reader missed the new wording, so for many SuperValu offers the Real Rewards member price was recorded as the price everyone pays. We fixed the reader and corrected 161,002 records on 18 October 2026.

• Tesco clearance, June to 15 October 2026: clearance prices recorded as shelf prices. Some Tesco "Reduced to Clear" prices were recorded without the clearance label. On 22 October 2026 we labelled 37,617 records as clearance.

• Aldi specials, to 21 October 2026: offers recorded without their saving, and prices before launch. Aldi shows the was price and saving of its specials only later in the day, so some were recorded at their offer price with no offer, and some products carried a placeholder price before they went on sale. On 22 October 2026 we added the was price and saving to 3,276 records and removed 402 placeholder records.

• Tesco Clubcard prices, 27 May to 27 October 2026: recorded a day early. Tesco lists Clubcard prices that start the next day, and we recorded some of them as the current day's price. We corrected 30,250 records on 27 October 2026.

• Dunnes Stores and SuperValu unit prices, to 14 October 2026: per gram read as per 100 g. For about 1,200 small products priced per gram or millilitre, the price per 100 g or 100 ml was recorded 100 times too low. We corrected 138,614 records on 14 October 2026.

See also How BasketWatch uses sources and our methodology.