9.3 Evaluating Variables Sampling Results & Upper Misstatement Limits

9.3 Evaluating Variables Sampling Results & Upper Misstatement Limits

Core Principle: Once an auditor completes substantive testing of sample items in Monetary Unit Sampling (MUS), the audit evidence must be mathematically evaluated to determine the Upper Misstatement Limit (UML)—the maximum monetary overstatement that could exist in the population at the specified risk of incorrect acceptance. The auditor compares the UML against the planned Tolerable Misstatement. If UML ≤ Tolerable Misstatement, the population is accepted as fairly stated; if UML > Tolerable Misstatement, the auditor must take definitive corrective audit actions under AU-C 530 and AU-C 450.

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1. The Mathematics of Tainting & Projected Misstatements

When a misstatement is discovered in an MUS sample item, the evaluation method depends entirely on whether the item's recorded book value is smaller than or greater than or equal to the Sampling Interval.

                                    EVALUATION BIFURCATION IN MUS
                                                  |
                   +------------------------------+------------------------------+
                   |                                                             |
      [ BOOK VALUE < SAMPLING INTERVAL ]                            [ BOOK VALUE ≥ SAMPLING INTERVAL ]
                   |                                                             |
      Calculate Tainting Percentage:                                No Tainting Calculation!
      Tainting % = (Book - Audited) / Book                          Projected Misstatement =
                   |                                                Actual Detected Misstatement
      Projected Misstatement =                                                   |
      Tainting % × Sampling Interval                                No Sampling Risk Attached
                   |                                                (Item is audited 100%)
      Subject to Incremental Allowance

Category 1: Items Smaller Than the Sampling Interval (BV < SI)

Because an item smaller than the sampling interval represents not only itself but an entire interval of unexamined dollars, any detected error must be converted into a percentage—known as the tainting percentage—and projected across the entire interval:

$\text{Tainting Percentage} = \frac{\text{Recorded Book Value} - \text{Audited Value}}{\text{Recorded Book Value}}$

$\text{Projected Misstatement} = \text{Tainting Percentage} \times \text{Sampling Interval}$

Example: An auditor finds an accounts receivable balance with a recorded book value of $2,000 and an audited value of $1,500. The sampling interval is $50,000.

• Tainting %: ($2,000 - $1,500) / $2,000 = $500 / $2,000 = 25%
• Projected Misstatement: 25% × $50,000 = $12,500

Category 2: Items Equal to or Larger Than the Sampling Interval (BV ≥ SI)

Items with book values equal to or exceeding the sampling interval are audited with 100% certainty. They do not represent other unexamined dollars. Therefore:

• No tainting percentage is calculated.
• The projected misstatement is simply the actual dollar misstatement detected in that item.
• No incremental allowance for sampling risk is applied to these items.

Example: An item has a recorded book value of $80,000 (where SI = $50,000) and an audited value of $74,000.

• Actual Misstatement = $80,000 - $74,000 = $6,000
• Projected Misstatement = $6,000 (exactly the actual misstatement; no projection across the interval).

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2. Structure of the Upper Misstatement Limit (UML)

The Upper Misstatement Limit (UML) consists of three distinct mathematical components:

$\text{Upper Misstatement Limit (UML)} = \text{Basic Precision} + \text{Total Projected Misstatement} + \text{Incremental Allowance for Sampling Risk}$

+-------------------------------------------------------------------------------------------------------+
|                             THREE LAYERS OF THE UPPER MISSTATEMENT LIMIT                              |
|                                                                                                       |
|   1. BASIC PRECISION (BP)              2. PROJECTED MISSTATEMENT (PM)   3. INCREMENTAL ALLOWANCE (IA) |
|   Reliability Factor (0 errors)        Sum of projected misstatements   Additional cushion for        |
|   multiplied by Sampling Interval.     from items < SI plus actual      sampling risk created by      |
|   Represents sampling risk even if     misstatements from items ≥ SI.   ranked tainting percentages   |
|   ZERO errors are found.                                                exceeding expected precision. |
+-------------------------------------------------------------------------------------------------------+

Component 1: Basic Precision (BP)

Basic Precision is the minimum allowance for sampling risk built into the sample design. Even if the auditor examines every sample item and finds zero misstatements, sampling risk still exists because not every dollar in the population was examined:

$\text{Basic Precision} = \text{Reliability Factor at Zero Errors} \times \text{Sampling Interval}$

For a 5% risk of incorrect acceptance (where RF₀ = 3.00) and a sampling interval of $50,000: $\text{Basic Precision} = 3.00 \times \$50,000 = \$150,000$

Component 2: Total Projected Misstatement

The sum of all projected misstatements for items smaller than the sampling interval plus the actual misstatements for items larger than or equal to the sampling interval.

Component 3: Incremental Allowance for Sampling Risk (IA)

When misstatements are found in items smaller than the sampling interval, the auditor must add an incremental cushion for sampling risk. To calculate this:

1. Rank all items smaller than the sampling interval in descending order of tainting percentage (highest tainting first).
2. Look up the incremental changes in the reliability factors (ΔRF) for each successive error.
3. Compute the incremental allowance for each error: (ΔRF - 1.00) × Projected Misstatement.

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3. Comprehensive Step-by-Step UML Calculation Walkthrough

An auditor conducts an MUS sample of accounts receivable with the following parameters:

• Sampling Interval ($SI$): $40,000
• Acceptable Risk of Incorrect Acceptance: 5%
• Reliability Factors (at 5% risk):
  • 0 misstatements: 3.00
  • 1 misstatement: 4.75 (ΔRF₁ = 4.75 - 3.00 = 1.75)
  • 2 misstatements: 6.30 (ΔRF₂ = 6.30 - 4.75 = 1.55)
  • 3 misstatements: 7.76 (ΔRF₃ = 7.76 - 6.30 = 1.46)
• Tolerable Misstatement: $180,000

The auditor tests the sample and identifies four misstatements:

Step 1: Calculate Basic Precision

$\text{Basic Precision} = 3.00 \times \$40,000 = \$120,000$

Step 2: Project Misstatements & Calculate Incremental Allowances

Rank the items with BV < SI by tainting percentage in descending order:

Rank 1: Account A (Tainting = 0.50)
        Projected Misstatement = 0.50 × $40,000 = $20,000
        ΔRF₁ = 1.75
        Incremental Factor = 1.75 - 1.00 = 0.75
        Incremental Allowance = 0.75 × $20,000 = $15,000

Rank 2: Account B (Tainting = 0.20)
        Projected Misstatement = 0.20 × $40,000 = $8,000
        ΔRF₂ = 1.55
        Incremental Factor = 1.55 - 1.00 = 0.55
        Incremental Allowance = 0.55 × $8,000 = $4,400

Rank 3: Account C (Tainting = 0.10)
        Projected Misstatement = 0.10 × $40,000 = $4,000
        ΔRF₃ = 1.46
        Incremental Factor = 1.46 - 1.00 = 0.46
        Incremental Allowance = 0.46 × $4,000 = $1,840

Item BV ≥ SI: Account D
        Projected Misstatement = $8,000 (Actual Misstatement)
        Incremental Allowance = $0 (100% audited; no sampling risk)

Step 3: Sum the Totals to Determine UML

$\text{Total Projected Misstatement} = \$20,000 + \$8,000 + \$4,000 + \$8,000 = \$40,000$

$\text{Total Incremental Allowance} = \$15,000 + \$4,400 + \$1,840 = \$21,240$

$\text{Upper Misstatement Limit (UML)} = \$120,000\text{ (BP)} + \$40,000\text{ (PM)} + \$21,240\text{ (IA)} = \$181,240$

Step 4: Compare UML to Tolerable Misstatement (Decision Rule)

• Upper Misstatement Limit: $181,240
• Tolerable Misstatement: $180,000

$\$181,240 > \$180,000 \longrightarrow \text{POPULATION CANNOT BE ACCEPTED AS FAIRLY STATED!}$

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4. The Authoritative Audit Decision Rule

Under AU-C 530, the statistical evaluation yields an unequivocal decision rule:

+-------------------------------------------------------------------------------------------------------+
|                                    THE SAMPLING DECISION RULE                                         |
|                                                                                                       |
|   If UML ≤ Tolerable Misstatement:                                                                    |
|   --> ACCEPT the recorded balance. The auditor has obtained reasonable assurance that the             |
|       account is not materially misstated.                                                            |
|                                                                                                       |
|   If UML > Tolerable Misstatement:                                                                    |
|   --> REJECT the recorded balance. The auditor cannot conclude that the account is fairly stated       |
|       at the planned level of sampling risk.                                                          |
+-------------------------------------------------------------------------------------------------------+

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5. Auditor Action Protocols When Sample Results Fail

When the Upper Misstatement Limit exceeds Tolerable Misstatement, GAAS strictly prohibits the auditor from ignoring the result or arbitrarily increasing tolerable misstatement. The auditor must execute a structured sequence of professional actions:

+-------------------------------------------------------------------------------------------------------+
|                             AUDITOR ACTION PROTOCOL UPON SAMPLE FAILURE                               |
|                                                                                                       |
|   STEP 1: INVESTIGATE CAUSES       STEP 2: CLIENT ADJUSTMENT        STEP 3: EXPAND SAMPLE / PROCEDURES|
|   Analyze underlying reasons for   Request client investigate       Expand sample size or perform     |
|   misstatements (clerical vs bias). full population & adjust        targeted alternative procedures   |
|                                    known misstatements.             on high-risk sub-populations.     |
|                                                                                                       |
|   STEP 4: PROPOSE FORMAL AUDIT ADJUSTMENT       STEP 5: MODIFY AUDIT OPINION (IF UNADJUSTED)          |
|   Calculate recommended adjustment to reduce    Qualified or Adverse opinion if management            |
|   remaining projected misstatement below TM.    refuses to record necessary audit adjustments.        |
+-------------------------------------------------------------------------------------------------------+

Step-by-Step Response Protocol

1. Investigate the Nature and Cause of Misstatements: Inquire of client personnel to identify why errors occurred (e.g., breakdown in cutoff controls, software billing glitch, or clerk misunderstanding credit terms).
2. Request Client Investigation and Adjustment: Present known misstatements to management. Request that management examine the entire transaction cycle, correct the known errors, and determine whether systematic adjustments are required across the ledger.
3. Perform Additional Substantive Procedures or Expand Sample:
   • The auditor may perform extended substantive testing in the specific areas where misstatements concentrated.
   • Expanding the sample may reduce the precision interval, but if misstatements continue at the same rate, expanding the sample will not rescue a failing sample.
4. Propose an Audit Adjustment: If management records an adjustment for the known misstatements and isolated systematic errors, the remaining projected misstatement may drop below tolerable misstatement, allowing the auditor to accept the adjusted balance.
5. Evaluate Impact on the Auditor's Report: If management refuses to adjust the financial statements and the uncorrected misstatement remains material, the auditor must issue a Qualified Opinion (material but not pervasive) or an Adverse Opinion (material and pervasive) under AU-C 705.

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6. Qualitative Evaluation of Misstatements: Error vs. Fraud

Under AU-C 450 (Evaluation of Misstatements Identified During the Audit) and AU-C 240 (Consideration of Fraud in a Financial Statement Audit), the auditor's evaluation of misstatements cannot be purely mathematical:

                                    QUALITATIVE MISSTATEMENT ASSESSMENT
                                                     |
                    +--------------------------------+--------------------------------+
                    |                                                                 |
           [ UNINTENTIONAL ERROR ]                                           [ INTENTIONAL FRAUD ]
                    |                                                                 |
       - Clerical data entry slip                                        - Intentional management override
       - Inadvertent mathematical oversight                              - Forged documentation / side letters
       - Isolated misunderstanding of terms                              - Fictitious entries near period-end
                    |                                                                 |
       AUDITOR RESPONSE:                                                 AUDITOR RESPONSE:
       Standard quantitative projection &                                Pervasive breakdown! Re-evaluate
       potential routine book adjustment.                                RMM, reconsider management integrity,
                                                                         and ESCALATE DIRECTLY TO AUDIT COMMITTEE!

Critical Qualitative Indicators

• Pattern vs. Randomness: Are misstatements random isolated slips, or do they all skew in the direction of increasing client revenue or gross margin?
• Management Involvement: Did misstatements originate from low-level clerical processing or from journal entries authorized by executive management?
• Contractual & Financial Impacts: Does the misstatement convert an earnings decrease into an earnings increase? Does it preserve compliance with debt covenants or trigger executive performance bonuses?
• Mandatory Escalation: If a misstatement indicates intentional fraud involving senior management, quantitative materiality is completely irrelevant—the matter must be reported directly to Those Charged With Governance (the Audit Committee) immediately.