Methodology: how we measure prices
This page explains where the numbers on each product page come from, how often we take them and what exactly they mean. If anything we publish does not match what it says here, that is our mistake and we want to hear about it.
What we measure, and how often
Once a day we take the price of every product at every shop that lists it and store it with its date. We never delete points or correct the series retroactively: whatever we recorded on a given day stays as recorded, even if it later turns out to have been a one-hour promotion.
We currently track 155 products across 5 categories, with 7,763 price observations recorded. The median series is 58 days long; the longest is 62.
Sources
Prices come from the official catalogues of the affiliate networks we work with: AliExpress, Kaspersky - ES. We do not scrape shop websites and we do not copy prices from other comparison sites.
The price we show is the shop’s price at the time of our last reading, with that date visible on the page. If the reading is more than 14 days old we stop asserting it as structured data: we still display it, but we do not ask Google to publish it as a live offer.
What each figure means
- Lowest recorded price
- The lowest price we have seen since we started tracking that product, with its date. We do not say “all-time low” until we have 90 days of history: before that the page says “lowest in N days”, which is what we actually know.
- 30 / 90 / 365-day average
- Arithmetic mean of the prices recorded in that window. If the series is shorter than the window, we average what we have and state how many days that is.
- Percentile of the current price
- What share of recorded days had a price lower than today’s. 20% means today’s price sits in the most expensive 20% of its own history. It is the number that best answers “is this cheap?”, because it does not depend on discounts announced by the shop.
- Significant change
- A move of at least 5% from the last price we already counted as a change. The threshold is not arbitrary: in this catalogue the median daily change is 0% and the 75th percentile is 0.48%, while the 90th percentile jumps to 8.24%. Either it does not move or it really moves; 5% falls in the gap. Counting currency-conversion cents as a “price change” would only add noise.
- Typical variation
- Median of the absolute daily change. It tells you whether the price is steady or jumpy.
- Our rating (1-5)
- It is a computed score, not the opinion of someone who has used the product: it comes from where the current price sits within its own history and how much data we have. That is why we do not publish it as a review in structured data — calling a formula a review would not be honest, and we have no user reviews to aggregate.
When we assert nothing
We need at least 7 days of history before a page talks about lows and averages. Below that we say we have just started tracking the product, because an “all-time low” based on three days of data means nothing.
Our relationship with the shops
We earn a commission if you buy through our links, at no extra cost to you. That does not change the price we show or the order the shops appear in: we always highlight the lowest real price we have read. We also do not accept payment to include a product or to improve its rating, which is a formula rather than an editorial decision anyway.
Links to shops carry rel="sponsored nofollow" and go through a redirector we do not index, so it is clear to anyone — reader or search engine — which links are commercial.
Mistakes
A feed can carry a wrong price, the wrong currency or a product that no longer exists. When we spot it we correct the data going forward and leave the past series untouched. If you see something that does not add up, get in touch.