fcsc_ipi_backend/ipi-methodology-cross-verification.md

IPI Methodology Cross Verification (Updated)

Scope

Cross-verification between:

• Annex V - IPI Calculation Methodology.pptx
• Current implementation in app/services/ipi_calculation_service.js
• Runtime trigger/orchestration in server.js and app/services/scheduler.service.js

Trigger Path Verification

Verified start path:

• server.js boots scheduler via scheduler.start().
• Cron 0 2 * * * executes runScheduledTask().
• runScheduledTask() calls executeCalculateQuarter(year, quarter).
• executeCalculateQuarter() runs runCompleteCalculation(year, month) for each month.
• Manual endpoint POST /api/admin/trigger-scheduler triggers same scheduler flow.

Status: MATCH

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Overall Conclusion

Current code is largely aligned on formula chain, with two remaining methodology gaps:

1. product-to-ISIC4 mapping source is still an approximation (derived from establishment submissions, not a fixed official mapping table),
2. non-response imputation rules from PPT are not implemented in this service.

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Verification Matrix (Current Code vs PPT)

1) Base-year average production

PPT (Slides 9-10):

• Base year average uses arithmetic mean of 12 months.

Implementation:

• calculateBaseYearProduction() computes average across Jan-Dec and stores in base_year_production.avg_by_production.

Status: MATCH

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2) Item-level index formula

PPT (Slides 8-10):

• Ri = CurrentProduction / BaseYearAverage
• Ii = Ri * 100

Implementation:

• calculateItemLevelIndices():
  • production_relative = current_production / base_year_avg_production
  • item_index = production_relative * 100

Status: MATCH

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3) ISIC 4-digit aggregation

PPT (Slides 11-12):

• Laspeyres weighted aggregation:
  • ISIC4 = SUM(w_i * I_i) / SUM(w_i)

Implementation (current):

• Uses weighted formula with products.weight_in_ib:
  • total_weight = SUM(weight_in_ib)
  • weighted_index_sum = SUM(weight_in_ib * item_index)
  • isic_4digit_index = weighted_index_sum / total_weight
• Prevents row multiplication by selecting one ISIC4 per product in-period using ranked mapping.

Status: PARTIAL MATCH (Formula MATCH, Mapping APPROXIMATION)

Reason for partial:

• Formula is aligned.
• Mapping source is not a fixed product master/official bridge; it is inferred from establishment-level submissions.

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4) ISIC 3-digit aggregation

PPT (Slide 13):

• Weighted roll-up from ISIC4.

Implementation:

• ISIC3 = SUM(total_weight_4 * isic_4digit_index) / SUM(total_weight_4)

Status: MATCH (depends on ISIC4 inputs)

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5) ISIC 2-digit aggregation

PPT (Slide 14):

• Weighted roll-up from ISIC3.

Implementation:

• ISIC2 = SUM(total_weight_3 * isic_3digit_index) / SUM(total_weight_3)

Status: MATCH (depends on ISIC3 inputs)

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6) Manufacturing IPI (headline)

PPT (Slide 15):

• Weighted roll-up from ISIC2.

Implementation:

• ManufacturingIPI = SUM(total_weight_2 * isic_2digit_index) / SUM(total_weight_2)

Status: MATCH

Note:

• Current code includes defensive handling when no valid ISIC2 aggregates exist for a month.

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7) Growth rates

PPT (Slide 16):

• YoY: ((Current - SameMonthLastYear) / SameMonthLastYear) * 100

Implementation:

• YoY formula matches.
• MoM is also computed additionally.

Status:

• YoY MATCH
• MoM Additional (not conflicting)

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8) Missing/non-response data treatment

PPT (Slide 3):

• For missing data, estimate using:
  • previous month repeat, or
  • average of last 3 months, or
  • same month previous year.

Implementation:

• This imputation logic is not implemented in the IPI service pipeline.
• Pipeline uses available approved records.

Status: MISMATCH

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Final Assessment (Current Code)

If Annex V is interpreted strictly:

• Formula chain: mostly aligned now (item -> ISIC4 -> ISIC3 -> ISIC2 -> headline).
• Remaining non-compliance points: official deterministic item/product-to-ISIC mapping source and missing-data imputation policy.

Practical statement for stakeholders:

• Current implementation is operationally correct and mathematically aligned for weighted aggregation, but still requires data governance alignment (official mapping + imputation policy) for full Annex V compliance.