Statistical Functions
Advanced
STDEV Function
The same spread as VAR, back in units you can read.
Task:
The same five lead times. Put their standard deviation in B7 — this time the answer comes back in days.
Learning Objectives:
- Compute a standard deviation with STDEV
- Relate it to the variance as its square root
- Express spread in the original units
Hints
Solve without hints for +5 XP
The data in this exercise
This is the grid you start with. Cell references in the task — B6, C2 — point at the row numbers and column letters below.
| A | B | |
|---|---|---|
| 1 | Month | Lead time (days) |
| 2 | January | 9 |
| 3 | February | 14 |
| 4 | March | 7 |
| 5 | April | 16 |
| 6 | May | 4 |
| 7 | Standard deviation |
What this exercise teaches (contains the answer)
The variance was 24.5 days-squared; the standard deviation is its square root, about 4.95 days. That is a number you can put in a sentence: lead times average 10 days, give or take about 5. For data that clusters around its mean, roughly two thirds of values fall within one standard deviation of it, so this is realistically a 5-to-15 day supplier — a very different thing to promise a customer than 10.