Did quality improve between the two lots?
You review two closed lots of divider cards at the fictional Alder Paper Works.
The question
Each lot contains 200 distinct starts. The first-pass yield target is 90%. Final yield includes cards accepted after approved rework.
| Lot A | Lot B | |
|---|---|---|
| Passed first check | 184 | 174 |
| Accepted after rework | 12 | 23 |
| Rejected | 4 | 3 |
Each started card has one outcome in the table.
“Compare the lots, then decide what evidence the quality lead should review.”
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A strong answer, step by step
Open each step in turn. This is one strong answer, not the only one.
Step 1: What passed on the first try?
What would you do here? Open the move you’d make.
Divide first-check passes by all accepted cards
Tempting, but it misses something. That leaves rejected units out of the denominator. Use all 200 starts.
Use distinct starts for both yield measures
The strong move. The first numerator counts first-check passes. The final numerator also counts accepted rework.
Count every successful rework as a new start
Tempting, but it misses something. Those units are already part of the original lot.
See how a strong candidate says it
“First-pass yield is 92% in A and 87% in B. Final yield is 98% in A and 98.5% in B.”
Why it works: Both rates use the number of distinct starts. Only final yield includes rework that passed.
Step 2: What do you tell the lead?
What would you do here? Open the move you’d make.
Report an improvement because fewer cards were rejected
Tempting, but it misses something. The lower rejection count does not explain why more units missed the first check.
Report both yields and investigate the first-check failures
The strong move. This keeps the delivery outcome and the growing rework burden visible.
Report a first-pass decline of 0.5 percentage points
Tempting, but it misses something. That is the change in final yield, with the opposite direction.
See how a strong candidate says it
“Final yield rose 0.5 percentage points. First-pass yield fell five points and missed the target. Lot B had 11 more successful reworks. I would look for where initial failures increased.”
Why it works: Final acceptance improved slightly while the number of cards needing another check went up.
Step 3: Where did the increase occur?
Both lots had 100 blue and 100 clear cards. A had 12 blue and four clear first-pass failures. B had 22 blue and four clear.
What would you do here? Open the move you’d make.
Compare the first-check rates within each color
The strong move. The blue group accounts for the whole increase in failures.
Treat the whole lot as if both colors had the same decline
Tempting, but it misses something. The clear group had the same rate in both lots.
Blame a larger share of blue cards in lot B
Tempting, but it misses something. Each lot had the same number of blue cards.
See how a strong candidate says it
“Blue first-pass yield fell from 88% to 78%. Clear stayed at 96%. I would check the blue units first.”
Why it works: The lot mix is the same. All 10 additional first-pass failures are in the blue group.
Step 4: What should you test next?
Lot B’s blue cards had 50 starts of each artwork revision. Revision 2 had 18 first-pass failures. Revision 1 had four.
What would you do here? Open the move you’d make.
Count the first-pass failures by revision and check like inputs
The strong move. This targets the difference and gives the quality owner a way to check it.
Declare that revision 2 caused every blue failure
Tempting, but it misses something. Revision 1 also had failures, and the comparison has not isolated a cause.
Use the final yield to clear both revisions from review
Tempting, but it misses something. Rework can hide the initial failure pattern.
See how a strong candidate says it
“Revision 2 failed first check on 18 of 50 cards, or 36%. Revision 1 failed on four of 50, or 8%. I would ask the quality owner to compare the revisions under matched conditions.”
Why it works: The revision split gives a place to look. Other differences between the runs could still explain the result.
The answer, in short
- Decision
- Report both yields and investigate the increase in initial failures.
- Because
- Rework can preserve final output while the first pass gets worse.
- What would change it
- A matched check could change which revision or process step the lead investigates.
Common traps
- Use distinct starts as the denominator.
- Compare rates within the affected group.
Check your answer
- I calculated both yields.
- I checked the first-pass target.
- I located the change by color.
- I named evidence that could confirm the cause.
Last reviewed Nov 11, 2026