long-term-impact-evaluation

Business

Choose methods for measuring long-term product impact after or beyond an A/B test. Use when comparing long-term holdbacks, post-period analysis, continuous monitoring, CLV models, delayed effects, short-term versus long-term metric tradeoffs, or lower-cost alternatives to long-term holdbacks.

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Long-Term Impact Evaluation

Use this skill to choose a practical method for measuring product impact beyond the initial experiment window. It compares long-term holdbacks, post-period analysis, continuous monitoring, and customer lifetime value models.

Source Traceability

Primary source: Next-Level A/B Testing by Leemay Nassery. Guidance is transformed and paraphrased from Chapter 8 on long-term impact, short-term and long-term metric relationships, holdbacks, post-period analysis, continuous monitoring, and CLV models.

Related skills:

holdback-experiment-design for detailed holdback planning.
trustworthy-experiment-insights for result credibility and false positives.
experimentation-strategy-roadmap for cost, quality, and complexity tradeoffs.

Reference Routing

Need	Read
Long-term evaluation concepts	`references/core/knowledge.md`
Method selection and risk rules	`references/core/rules.md`
Scenario examples	`references/core/examples.md`
Step-by-step method selection	`workflows/choose-long-term-evaluation.md`

Workflow

State why short-term experiment metrics are insufficient.
Identify the expected time horizon and delayed mechanisms.
Compare holdback, post-period analysis, continuous monitoring, and CLV model options.
Weigh accuracy against user cost, business cost, complexity, and confounding.
Choose the simplest method that answers the long-term question.
Define metric cadence, interpretation limits, and follow-up decisions.

Output Format

# Long-Term Impact Evaluation Plan

## Long-Term Question
[What delayed or sustained effect must be measured.]

## Recommended Method
[Holdback | Post-period analysis | Continuous monitoring | CLV model | Hybrid]

## Tradeoffs
| Method | Benefit | Cost/Risk | Fit |
|--------|---------|-----------|-----|

## Measurement Plan
- Short-term metric:
- Long-term metric:
- Time horizon:
- Confounders:

## Decision Rules
- Continue measuring if:
- End or revise if:
- Escalate if:

Quality Bar

Do not create a long-term holdback when a lower-cost method can answer the decision well enough.
Do not use post-period analysis without accounting for external factors such as seasonality or campaigns.
Do not rely on CLV models without naming model drift and behavior-change risk.
Do not confuse continuous monitoring with causal long-term measurement.