Should weekends be staffed like any other day?
Twenty weekdays against eight weekend days of basket counts. Weekends run 63% heavier and, far more usefully, three and a half times less predictable, which is the number a staffing rota should be built on.
Operations Starter Statistics free
After you install, this is the model to open.
Weekday and Weekend Are Not the Same Business
- In your spreadsheet, click the Sortia icon in the strip of icons down the right-hand edge. No strip? Click the arrow at the bottom-right to open it. You can also use Extensions, then Sortia, then Open Sortia.
- Click Start from a template and put that name in the search box.
- Pick the card with that name and click Load this template. It arrives on a new tab with real numbers already in it.
The answer
- Weekend day
- 702 baskets, against 431 on a weekday
- The gap
- +63% t -11.24, p 0.00001, real beyond argument
- Weekend spread
- 3.6x sd 67.3 against 18.6, df 7.4 rather than 26
- Staff for
- 36.4 hours the busiest weekend day, not the 31.9 average
Twenty weekdays and eight weekend days of basket counts from the same store. Weekdays average 430.85 and weekends average 702.13. Click Run: t comes back -11.24 with a two-tail p-value of about 0.00001, and the test is a formality, because nobody in the building thought weekends were the same as weekdays. The result worth reading is the degrees of freedom: 7.43, not the 26 an equal-variances test would have used.
Welch has noticed that the weekend column varies three and a half times as much as the weekday column, standard deviations of 67.25 against 18.64, and has priced eight noisy days accordingly. That is the finding. A weekday is 430 baskets give or take twenty. A weekend day is 700 baskets give or take seventy, and the gap between the quietest Saturday in the sample at 615 and the busiest Sunday at 801 is 186 baskets, which is more than 40% of an entire weekday.
The staffing block at the side of the sheet turns that into a rota at 22 baskets a staffed hour: 19.6 hours covers an average weekday, 31.9 covers an average weekend day, and 36.4 covers the busiest weekend day seen here. Staff the weekend to its average and you are understaffed on roughly half of them, which is why weekend service complaints do not track weekend volume.
Rerun with the equal-variances test to see what you would otherwise have been told with a straight face: a much smaller p-value and 26 degrees of freedom that eight weekend days never earned. Welch is the right default for two samples of different sizes and different spreads, and this pair is both. What it cannot tell you is which weekends will be the big ones, because weather and payday are not in the columns.
To use your own store, split your days into two columns with a distinct heading on each, keep the two groups the lengths they really are, and widen both ranges.
The model
It arrives on a tab called Template: Weekday and Weekend, carrying these columns:
- Weekday
- Weekday baskets (count)
- Weekend day
- Weekend baskets (count)
- =AVERAGE(B2:B21)
with the model computed beside the data:
| Weekend average (baskets) | 702.1 |
| Weekday spread (baskets) | 18.64 |
| Weekend spread (baskets) | 67.25 |
| Weekday staff hours needed | 19.58 |
| Weekend staff hours needed | 31.91 |
| Weekend hours to cover the busiest day seen | 36.41 |
Once it is in your sheet
- The model arrives with real numbers in it and runs as it stands, so you can press the button first and understand it second.
- Change the numbers to yours. The sheet marks which cells are inputs and which hold formulas, and most labels carry a note explaining the row.
- Press the run button at the bottom of the panel. It is labeled for the tool you are in, and the result lands on its own tab, with a written reading of it beside the figures.
Never used Google Sheets? Start here goes the whole way, in seven steps, and assumes nothing.
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Every model like this one, and the method behind them: Statistics in Google Sheets.