More often than not, vendors were charging different prices for the same item on a given day. Only 36 per cent of items in our dataset were always sold at the same price, so nearly two thirds of ingredients showed some same-day price variation in the 90-day period. When vendors charge restaurants different prices for the same item on the same day, how large is the price difference? For all items that showed at least some price variation, we calculated the maximum same-day price difference observed over a 90-day period. The distribution of variation sizes is shown below.
Roughly one third of items shifted in price by less than 10 per cent of their average price. The remaining two thirds showed more dramatic price variations, with vendor prices varying up to 50 per cent for the same item between different restaurants on the same day. We next looked at which items vendors were most likely to sell for different prices on the same day. We divided the number of days on which we saw price variation by the total number of days that item was sold, and expressed the result as a percentage. The 25 items for which vendors’ prices shifted most dramatically in one day are ranked below.
The products with the most variable prices were diverse, encompassing produce, dairy, meats, and dry goods. For the products above, vendors charged prices that varied on 87 per cent or more of the days on which they were sold. The items we ranked above represent a range of categories. Does that mean that price variation is roughly as common in one category as in the next? To find out, we looked at the percent of products in each category that varied in price at least some of the time. Categories are ranked accordingly below.
Restaurants are most likely to encounter variation in vendor pricing when purchasing alcohol — nearly 60 per cent of the items in this category showed some price variation. Similarly, in the produce and non-alcoholic beverage categories, vendors charged different prices for more than 50 per cent of the items sold at least some of the time. Even in the categories where price variation was least prevalent — kitchen supplies and prepared foods — 20-25 per cent of products had shifting prices.
Prices for these top 25 products swung up to 52 per cent in a single day between different restaurants purchasing the exact same product from a given vendor. At the top of this ranking, for example, the cost of a chicken cutlet shifted by nearly a dollar within a single day. And some unlucky restaurateurs have paid up to $41.73 for dark brown sugar — ranked eighth on our list — while their neighbors paid just $28.73 from the same supplier.
For about 50 per cent of items, there was no relationship between price and volume purchased of that item. In other words, the price might have shifted, but not in a way that was correlated with purchase volume. Of the items that did show a relationship between price and quantity, we more often saw that high-volume purchases were priced lower — a trend that reflects bulk discounting.