Was your best day on site really your best?
Twenty-one days of drainage output tested against fences built from the run itself. Two days come back flagged and one of them is the good day, which is usually the more interesting of the pair.
Construction Starter Statistics free
After you install, this is the model to open.
Which Days on Site Went Wrong?
- 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
- Days flagged
- 2 of 21 outside fences of 51.5 and 71.5 meters
- The bad day
- 31 m score 5.6: ground water and a midday pump hire
- The best day
- 88 m score 4.8: an eight-person gang, not a fast one
- Per person that day
- 11.0 m 88 meters over eight people, below the usual rate
Twenty-one days of drainage from one gang, with the site diary alongside. Click Run: the fences come out at below 51.50 and above 71.50 meters, and two days are flagged, the 31-meter day with a score of 5.6 and the 88-meter day with a score of 4.8. Most people expect one flag and get two, and the second is the useful one. A bad day has an obvious cause and the diary already carries it, in this case ground water and a pump hired at midday.
The good day does not: 88 meters is not a gang that tried harder, it is a different gang, and the Gang size column says so, because eight people were on it instead of five. Per person that day produced 11.0 meters against the 12.3 the ordinary days deliver, so the best day in the run is slightly below average productivity and only looks exceptional because nobody normalized it.
That is the whole argument for testing outliers rather than eyeballing a chart. Delete the 88 and rerun and the fences tighten to below 52.63 and above 69.63, and the 31 still flags on its own, now with a score of 6.6. The fences are built from the middle half of your data, so the template needs no threshold from you and no calibration when the work changes from drainage to blockwork.
What it cannot tell you is whether a flagged day is an error in the measurement or a real event, and the only way to settle that is the diary beside it. To use your own run, paste daily output under Drainage laid, keep one row per working day in date order, keep the gang size in its own column outside the range so meters and people never share a column, and widen the input range.
The model
It arrives on a tab called Template: Which Site Days Went Wrong, carrying these columns:
- Date
- Drainage laid (linear m)
- Gang size (people)
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.