Module sampling_plan 

Audit sampling methodology models per ISA 530.

ISA 530 (Audit Sampling) requires the auditor to design and perform audit procedures to obtain sufficient appropriate audit evidence. The sampling plan documents the population, key items, methodology, and sample drawn.

Key concepts:

• Key items: 100% tested; amounts ≥ tolerable error, unusual or high-risk items.
• Representative sample: drawn from the residual population using a statistical or non-statistical method proportional to the CRA level.
• Monetary Unit Sampling (MUS): preferred for balance testing (existence, valuation) — each monetary unit has an equal probability of selection.
• Systematic selection: preferred for transaction testing — fixed interval with random start.

References:

• ISA 530 — Audit Sampling
• ISA 315 — links CRA level to sampling extent
• ISA 320 / ISA 450 — tolerable error equals performance materiality

Structs

KeyItem

A key item selected for 100% testing outside the representative sample.

SampledItem

A single item selected into the audit sample (key item or representative).

SamplingPlan

Audit sampling plan for a single account area / assertion combination.

Enums

KeyItemReason

Reason why an item was designated as a key item (100% tested).

SamplingMethodology

Sampling methodology chosen for the plan per ISA 530.A5–A8.

SelectionType

Whether an item was selected as a key item or a representative sample item.