Previously, I had posted on using box plots to estimate portions for kitchen prep.

In addition to estimating portions, a restaurant needs to anticipate how to staff each shift. As was the case with kitchen prep, box and whisker plots can help for staffing. By looking at the range of orders for shifts, you can estimate ‘how busy’ things might be. And by looking at net revenue, staffing requirements can be balanced with the cost of a higher head count.

Restaurant box plot - estimating workload

Unsurprisingly, Saturday evenings are the busiest and generate the most revenue. However, there is a wide range both above and below the median. You will want to staff more than other days, but how much? Depends on what you consider the greater risk. 1) Not having enough staff, and negatively impacting service and potentially repeat customers. Or 2) Being overstaffed and cutting into margins. (Or worse, cost exceeds net revenue.)

On the other hand, the range is quite narrow on other days, so estimating staff requirements will be easier. And Sunday is between the two extremes. Not as great a range as Saturday night, but still greater than weekdays. Unlike Saturday, the range is bottom heavy. (Data points are closer below and more spread out above. In this situation you can hedge your bets by sticking between the bottom and middle of the range.

How does a restaurant decide how many brussel sprouts portions to prep for any given shift? Prep too many and food gets thrown away, increasing costs. Prepping too many results in increased ticket times, which impacts service. Customers develop a negative impression as their orders are delayed.

Visualizing point-of-sale (POS) data can show historical purchase data to more accurately estimate needs. The box and whisker plot can display the variation in orders during different time periods. The box plot below shows how many brussel sprout portions, whether for a stand-alone order or as a side, were required for the morning and night shifts on each day of week.

Daily portions box and whisker plot for kitchen prep

A box plot provides more than simply looking at averages, which can be skewed by outliers. The bar portion of the graph shows how many portions were needed half the time. The center of the bar (where the color changes) shows the middle (median) portions needed. The bracket shows the top quarter and bottom quarter portion needs. By looking at the middle point and how far the box-and-whisker stretches from the middle, you estimate whether the portions required are more likely to be the lower quantities or the higher ones.

From this example, more of the shifts are bottom heavy. In these cases, it might be best to prep for a quantity around the median value. The Sunday morning shift, however, splits down the middle and covers a wide range. Whether you go with the lower or higher value depends on whether wastage or increased ticket times is of greater concern.

Another bit of information the box plot can provide are outliers. These are the data points that fall outside of the box and whisker. In this plot the Saturday night shift are all outliers, making it difficult to estimate the correct portion to prep. In this case, you might try looking at a plat that includes more POS data.