Define the question and the data contract
Define what you are counting before calculating an average.
Reviewed: 2026-10-03
Source-based teaching example · Fictional data
Narration: Microsoft Mark · locally synthesized

00:00:00.000 — What you will learn

Define what you are counting before calculating an average.

Visual description:
Define what you are counting before calculating an average.

00:00:06.417 — The idea

State what one row represents, the units and which rows belong in the question. Missing is different from zero. Report excluded or unresolved rows separately.

Visual description:
State what one row represents, the units and which rows belong in the question. Missing is different from zero. Report excluded or unresolved rows separately.

00:00:19.792 — One useful term

Denominator. The count or quantity you divide by when calculating a rate or average.

Visual description:
The count or quantity you divide by when calculating a rate or average.

00:00:28.500 — A worked example

Two closed requests took thirty and forty-five minutes. An open request has no duration. The closed-request mean is 37.5 minutes, using two observations.

Visual description:
Two closed requests took thirty and forty-five minutes. An open request has no duration. The closed-request mean is 37.5 minutes, using two observations.

00:00:43.667 — Your turn to think

Should the open request enter the completed-duration average as zero? Pause and decide before continuing.

Visual description:
Should the open request enter the completed-duration average as zero?
Pause the video if you need more time.

00:01:01.208 — Why this answer works

No. That changes the total you divide by and the meaning. The result describes only the two closed sample requests.

Visual description:
No. That changes the total you divide by and the meaning. The result describes only the two closed sample requests.

00:01:12.125 — Check 1

Define the row unit and question.

Visual description:
Define the row unit and question.

00:01:17.125 — Check 2

Separate open and invalid records.

Visual description:
Separate open and invalid records.

00:01:22.333 — Check 3

Keep missing values different from zero.

Visual description:
Keep missing values different from zero.

00:01:27.667 — Now try a different case

Open the lesson and try its different practice case. Use every check in the full task. Watching alone does not mark the lesson complete.

Visual description:
Open the lesson
Try the new case
Check and revise
The full task and its requirements are in the linked lesson.