Data Science Foundations: Practical Approaches with the 80/20 Rule – Part 2

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, we focused on the early stages of a data science project—setting clear goals, planning for deployment, and getting quick wins through smart data triage and cleaning. Now, we shift into the modeling and evaluation phase, where many projects get lost in complexity.

Here’s the truth:

80% of modeling value comes from just 20% of the techniques.

You don’t need to test 20 algorithms, optimize 50 hyperparameters, or chase the last decimal in accuracy. Doing so often delays value delivery and confuses your stakeholders.

This part will help you stay focused on impact, not complexity, by showing how to:

• Design efficient experiments
• Choose metrics that matter
• Deploy with speed and simplicity

? Design Experiments That Test What Matters


1. Too Many Models, Too Little Insight
It’s tempting to benchmark every algorithm in your toolbox. But in real-world data science, this is often a trap. More models ≠ better results. It just wastes time and obscures the signal.

80/20 Move: Start with one baseline + one power model (e.g., logistic regression + XGBoost).

2. Prioritize Strong Features Early
Don't chase marginal gains from obscure variables. The top 3–5 features often explain most of your target behavior.

? Start with variables tied directly to business logic (e.g., time since last purchase, product usage frequency).

3. Limit Your Feature Set to Force Focus
Try this: cap yourself at 10 features in early testing. This constraint will sharpen your thinking and surface truly important signals.

4. Use Hypotheses, Not Hunches
Before modeling, write out what you expect and why. Hypothesis-driven modeling keeps your experiments business-focused and honest.

5. Avoid the “Leaderboard” Mindset
You’re not on Kaggle. Iteration is fine, but obsessing over small AUC gains wastes time. If it doesn’t change a business decision, it doesn’t matter.

? Choose Evaluation Metrics That Reflect Real-World Impact


1. Accuracy Is Often Useless
In imbalanced data (e.g., churn, fraud), accuracy can be high even when your model is blind. Always look deeper.

A churn model with 95% accuracy might never predict churn, because only 5% of customers churn.

2. Use Precision, Recall, F1 for Classification
Choose based on what mistake costs more:

• False positives expensive? → Prioritize precision
• False negatives worse? → Focus on recall
• Both matter? → F1-score or PR curves

3. For Regression, Interpretability Beats Complexity
Business users often prefer:

• MAE for dollar-based errors
• MAPE when % errors are easier to digest
• Avoid RMSE unless you need to penalize large errors

4. Create Custom Business Metrics
For real impact, define metrics aligned with the outcome:

• Churn model: "Top 10% captures 40% of total churn"
• Lead scoring: "Top decile leads to 2x conversion"

? Always tie metrics back to decisions. What does your stakeholder do with this score?

5. Co-Define Success Metrics With Stakeholders
Don’t pick metrics alone. Before building anything, define what a “useful” model looks like with your business partner.

? Deploy Like a Pragmatist, Not a Perfectionist


1. Don’t Overengineer the First Version
A good-enough model in production is 100x more valuable than a perfect model on your laptop.

? Sometimes, a CSV emailed weekly is better than a dockerized endpoint.

2. Deploy in Stages

• First: static predictions to test business use
• ? Then: basic batch updates
• Later: automate if and only if there’s proven ROI

3. Start With the Tools the Business Uses
Your output should fit into existing workflows. Excel? Tableau? Google Sheets? That’s fine—use what works.

4. Monitor the Basics (Not Everything)
Even simple deployments need guardrails:

• Check for input drift
• Watch prediction distribution
• Track impact on KPIs

? Build a lightweight dashboard. Even a shared Google Sheet is a win.

5. Collaborate With Engineers Early
If you need to scale later, build bridges now. Align on formats, refresh schedules, and alerting.

Recap – Deliver More by Modeling Less


Here’s the 80/20 recap for modeling and evaluation:

• Focus your experiments on the most valuable variables and questions
• Pick metrics that drive decisions, not just charts
• Deploy as simply as possible, then iterate if it’s worth it

Most models fail not because they’re wrong, but because they were built in isolation, measured in a vacuum, or never deployed.

Stay outcome-driven. Focus on usefulness over elegance. Remember:

You’re not paid to build models—you’re paid to solve problems.

Next up in Part 3:
We’ll cover the final stretch—how to communicate like a strategist, manage expectations, and build lasting trust with stakeholders. Because a great model is worthless if nobody understands or uses it.

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