How the Cá Buồm index is built
The index answers one question: did the same basket of everyday goods get more expensive since yesterday. It is built from prices that shoppers actually see, not from a survey and not from news reports.
Where the prices come from
The calculation
- 1. Each day every product is matched to itself from the day before, by retailer article number. New and delisted products are ignored for that day, so a changing assortment cannot move the index.
- 2. For every matched pair we take the logarithm of the price ratio. If a product is on sale, the sale price counts, because that is what people pay. Ratios beyond threefold are dropped as data errors.
- 3. Those numbers are averaged inside each category, then categories are combined with fixed weights.
- 4. The result multiplies yesterday’s level. The first day of collection equals 100, so the number reads as a percentage against the start.
Category weights
Weights follow roughly how a Vietnamese household splits everyday spending. They are fixed, published here, and changed only with a note on this page.
What this is not
This is not the official inflation rate. The General Statistics Office publishes CPI once a month from its own nationwide survey, covering rent, services, healthcare and education that we do not track. Our index is narrower, faster and fully transparent: every number on this site can be traced back to a price on a shelf.
Using the data
Charts and figures may be quoted freely with a link to cabuom.com. Machine access, custom baskets and history exports for businesses are available on request through Telegram.
@cabuom