2nd/10_Wiki/Topics/AI_and_ML/Pareto-Principle.md

id, title, category, status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, verification_status, tags, raw_sources, last_reinforced, github_commit, tech_stack

id	title	category	status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	verification_status	tags	raw_sources	last_reinforced	github_commit	tech_stack
wiki-2026-0508-pareto-principle	Pareto Principle	10_Wiki/Topics	verified	self	80/20 Rule Pareto Distribution Power Law	none	A	0.9	applied	pareto 80-20 prioritization decision-making		2026-05-10	pending	language framework python pandas, numpy

Pareto Principle

매 한 줄

"매 80% of effects from 20% of causes". Vilfredo Pareto (1896) — 매 Italy land ownership 의 observation. 매 modern application: bug triage (top 20% bugs cause 80% crashes), customer revenue (top 20% pay 80%), feature importance (top 20% features carry 80% of model signal). 매 prioritization heuristic 의 default.

매 핵심

매 origin

• Pareto 1896: 매 80% of Italian land owned by 20% of population.
• Juran 1940s: 매 quality control — "vital few vs trivial many".
• 매 Power Law family — log-log linear distribution.
• 매 80/20 의 mnemonic 일 뿐 — 매 actual ratios vary (90/10, 70/30 등).

매 핵심 insight

• Effects are NOT uniformly distributed across causes.
• Sorting by impact 의 long tail 발견.
• ROI: 매 fix top 20% causes → solve 80% of problem with 20% of effort.
• Caveat: 매 remaining 20% of effects 매 important 일 수 있음 (safety, compliance).

매 software / ML context

• Bug triage: 매 small set of bugs causes most crashes.
• Performance hotspots: 매 5% of code = 95% of CPU time.
• Feature importance: 매 top features dominate model signal.
• Customer revenue: 매 enterprise tail tiny number of users.
• Test coverage: 매 80% of bugs in 20% of code paths.

매 응용

1. Backlog prioritization (impact × ease).
2. Performance profiling (optimize hot path first).
3. Feature engineering (drop low-importance features).
4. Customer success (focus on high-value accounts).
5. Bug fixing (top crash signatures first).

💻 패턴

Pareto chart for bug triage

import pandas as pd
import matplotlib.pyplot as plt

df = pd.DataFrame({"bug": ["A","B","C","D","E","F"],
                   "occurrences": [500, 300, 100, 50, 30, 20]})
df = df.sort_values("occurrences", ascending=False)
df["cum_pct"] = df["occurrences"].cumsum() / df["occurrences"].sum() * 100

fig, ax1 = plt.subplots()
ax1.bar(df["bug"], df["occurrences"])
ax2 = ax1.twinx()
ax2.plot(df["bug"], df["cum_pct"], "r-o")
ax2.axhline(80, color="gray", linestyle="--")
plt.show()

Find the "vital 20%"

def vital_few(values, threshold=0.8):
    sorted_vals = sorted(values, reverse=True)
    cumsum = 0
    total = sum(sorted_vals)
    for i, v in enumerate(sorted_vals, 1):
        cumsum += v
        if cumsum / total >= threshold:
            return i, sorted_vals[:i]
    return len(values), sorted_vals

Feature importance pruning

import xgboost as xgb
model = xgb.XGBClassifier().fit(X, y)
importance = pd.Series(model.feature_importances_, index=X.columns).sort_values(ascending=False)
cumulative = importance.cumsum() / importance.sum()
top_features = importance[cumulative <= 0.8].index  # vital few
print(f"{len(top_features)} of {len(X.columns)} features carry 80% importance")

Revenue concentration analysis

customers = pd.read_csv("customers.csv").sort_values("revenue", ascending=False)
customers["cum_revenue_pct"] = customers["revenue"].cumsum() / customers["revenue"].sum()
top_20 = customers.head(int(len(customers) * 0.2))
print(f"Top 20% generate {top_20['revenue'].sum() / customers['revenue'].sum():.0%}")

Profiling hot path (Python)

import cProfile, pstats
profiler = cProfile.Profile()
profiler.enable()
run_workload()
profiler.disable()
stats = pstats.Stats(profiler).sort_stats("cumulative")
stats.print_stats(20)  # top 20 functions usually = 80%+ time

LLM cost: top tokens

# 매 prompt token spend tracking
from collections import Counter
spend = Counter()
for log in logs:
    spend[log["prompt_template"]] += log["tokens"] * log["cost_per_token"]
total = sum(spend.values())
running = 0
for template, cost in spend.most_common():
    running += cost
    print(f"{template}: ${cost:.2f}, cumulative {running/total:.0%}")
    if running/total > 0.8: break

매 결정 기준

상황	Approach
Backlog overload	Pareto-rank by impact, ship top 20%
Slow application	Profile, fix hot path 먼저
Too many features	Importance-based pruning
Customer support	Tier by revenue, allocate AE coverage
Long bug list	Triage by frequency × severity
Compliance / safety	Pareto NOT applicable (매 100% 필수)

기본값: 매 sort by impact, take top until cumulative ≥ 80%.

🔗 Graph

• 부모: Power-Law
• 변형: 80/20 Rule · Long-Tail
• 응용: Feature-Importance

🤖 LLM 활용

언제: 매 backlog prioritization, optimization scope, feature selection, customer segmentation. 언제 X: 매 safety-critical / compliance — long tail 매 ignore 불가.

❌ 안티패턴

• Treating 80/20 literally: 매 actual ratio varies — measure, don't assume.
• Ignoring long tail entirely: 매 some long-tail items high-leverage (zero-day, churn-risk customer).
• Cause/effect confusion: 매 20% of features cause 80% of accuracy ≠ keep only those (interactions matter).
• Static analysis: 매 Pareto re-ranks over time — 매 weekly recompute.
• Pareto in safety domain: 매 medical, finance, security — 매 100% coverage 필수.

🧪 검증 / 중복

• Verified (Pareto 1896 Cours d'économie politique, Juran 1951 Quality Handbook).
• 신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — Pareto applications, charts, anti-patterns