Find the few causes behind most defects, errors or returns

Analyze the log below and find which causes account for most of the problems, for {{audience}} to decide what to fix first. I need a ranked count of causes with the share each makes up (a Pareto analysis), not a general list of quality tips.

Defect, error or return log for {{period}} (date, product or process, defect type or reason, quantity, cost if known, notes):
"""
{{defect_log}}
"""

Total units produced, orders shipped or transactions processed in the period: {{volume}}
Our standard list of defect types, if we have one: {{categories}}

Steps:
1. Group the entries into defect types. Use our list if given. If the log uses free text, group similar descriptions and show the grouping as a table with the columns Group, Raw descriptions, Entries, so it can be checked.
2. Count each type by quantity, and by cost where costs are given. If an entry has no quantity, count it as 1 and say how many you counted that way. If only some entries have a cost, total cost only for those and say how many lack one.
3. Rank the types and add a running percentage.

Produce:
1. A table with the columns Defect type, Count, % of total, Running %, Cost (if known). Keep "Unclassified" as the last row whatever its size, and say if it is over 10% of the total.
2. The vital few: the types that make up about 80% of the total, in one sentence, for example "Three of 11 defect types (wrong labels, short picks and crushed corners) make up 78% of returns." If no small group reaches about 80%, say so plainly rather than forcing one.
3. Overall defect rate: total defects / volume, with the calculation, only if both are in the same unit (units against units, orders against orders); otherwise say what figure is needed.
4. Patterns worth checking: up to 5, such as a type concentrated on one line, shift, product or week, each with the counts behind it.
5. Next questions: what to look at to find the root cause of the top types.

Rules:
- Count only what the log shows, and make sure the counts add up to the total quantity in the log.
- Do not state causes behind the defect types. Patterns are leads to check, not conclusions.
- Keep the text outside the tables under 250 words.

If an entry is unclear or could belong to two groups, put it in "Unclassified" rather than forcing it into a group.