Metric Reconciliation

Quick Start

Systematically compare metrics across different data sources, identify discrepancies, investigate root causes, and produce reconciliation reports with actionable fixes.

Context Requirements

Before reconciling metrics, I need:

1. Data Sources: The 2+ systems/datasets to compare
2. Metric Definitions: How each source calculates the metric
3. Expected Variance: What difference is acceptable vs. concerning
4. Time Period: What date range to reconcile
5. Join Keys: How to match records across sources

Context Gathering

For Data Sources:

"I need access to the data from each source. Please provide:

Source 1 (e.g., Production Database):

• Connection details OR CSV export OR SQL query to fetch data
• System name: 'Postgres Production DB'
• What metric: 'Total Revenue'

Source 2 (e.g., Analytics Warehouse):

• Connection details OR CSV export OR SQL query to fetch data
• System name: 'Snowflake Analytics'
• What metric: 'Total Revenue'

Additional Sources (if comparing 3+ systems):

• Same information for each additional source

Can you provide data exports or connection details for each source?"

For Metric Definitions:

"To understand why metrics might differ, I need:

How is the metric calculated in each source?

Example for 'Total Revenue':

• Source 1 (Production): SUM(orders.total_amount) WHERE status = 'completed'
• Source 2 (Analytics): SUM(daily_revenue.amount) WHERE type = 'sale'

Known calculation differences:

• Does Source 1 include refunds? (yes/no)
• Does Source 2 exclude certain transaction types? (which ones?)
• Different time zones? (UTC vs EST)
• Different granularity? (transaction-level vs daily aggregates)

Understanding these helps identify expected vs. unexpected differences."

For Expected Variance:

"What variance is acceptable before we investigate?

Common Thresholds:

• Financial metrics (revenue, payments): <0.1% variance acceptable
• User metrics (signups, sessions): <2% variance acceptable
• Behavioral metrics (clicks, views): <5% variance acceptable

For your metric, what % difference would trigger investigation?

Also:

• Are some time periods expected to differ? (recent data still syncing?)
• Known lag between sources? (e.g., data warehouse updates daily)"

For Time Period:

"What time range should I reconcile?

Options:

• Specific dates: '2024-12-01' to '2024-12-31'
• Last N days: Last 7 days, last 30 days
• Relative period: Last month, last quarter
• All time: Full historical comparison

Note: Longer periods may take more time but show trends in variance."

For Join Keys:

"How should I match records between sources?

Common Join Strategies:

1. Aggregate Comparison (simplest):

   • Compare totals only
   • Example: Total revenue Source 1 vs Source 2

2. Time-Based Comparison:

   • Match by date/hour/minute
   • Example: Daily revenue Source 1 vs Source 2

3. Entity-Based Comparison:

   • Match by transaction ID, order ID, customer ID
   • Example: Order #12345 in both systems

4. Multi-Key Comparison:

   • Match by date + entity
   • Example: Customer X's revenue on 2024-12-15

Which approach makes sense for your use case?"

Workflow

Step 1: Load Data from Each Source

import pandas as pd
import numpy as np
from datetime import datetime, timedelta

# Load Source 1
if source1_type == 'database':
    source1_df = pd.read_sql(source1_query, source1_connection)
elif source1_type == 'csv':
    source1_df = pd.read_csv(source1_file)

# Load Source 2
if source2_type == 'database':
    source2_df = pd.read_sql(source2_query, source2_connection)
elif source2_type == 'csv':
    source2_df = pd.read_csv(source2_file)

print(f"📊 Data Loaded:")
print(f"  Source 1 ({source1_name}): {len(source1_df):,} records")
print(f"  Source 2 ({source2_name}): {len(source2_df):,} records")

Checkpoint: "Data loaded successfully. Record counts look reasonable?"

Step 2: Standardize Data Formats

def standardize_data(df, date_col, metric_col, source_name):
    """Standardize data format for comparison"""
    
    # Convert dates to datetime
    df[date_col] = pd.to_datetime(df[date_col])
    
    # Ensure metric is numeric
    df[metric_col] = pd.to_numeric(df[metric_col], errors='coerce')
    
    # Remove nulls
    original_count = len(df)
    df = df.dropna(subset=[date_col, metric_col])
    dropped = original_count - len(df)
    
    if dropped > 0:
        print(f"⚠️  {source_name}: Dropped {dropped} records with null date/metric")
    
    # Add source identifier
    df['source'] = source_name
    
    return df

source1_df = standardize_data(source1_df, 'date', 'revenue', 'Source1')
source2_df = standardize_data(source2_df, 'date', 'revenue', 'Source2')

Step 3: Aggregate at Comparison Level

# Aggregate by date (or whatever join key you're using)
source1_agg = source1_df.groupby('date')['revenue'].sum().reset_index()
source1_agg.columns = ['date', 'source1_revenue']

source2_agg = source2_df.groupby('date')['revenue'].sum().reset_index()
source2_agg.columns = ['date', 'source2_revenue']

print(f"\n📈 Aggregated Data:")
print(f"  Source 1: {len(source1_agg)} date periods")
print(f"  Source 2: {len(source2_agg)} date periods")

Step 4: Join and Compare

# Full outer join to catch records in one source but not the other
comparison = source1_agg.merge(source2_agg, on='date', how='outer')

# Fill NaN with 0 for missing dates
comparison['source1_revenue'] = comparison['source1_revenue'].fillna(0)
comparison['source2_revenue'] = comparison['source2_revenue'].fillna(0)

# Calculate differences
comparison['difference'] = comparison['source1_revenue'] - comparison['source2_revenue']
comparison['abs_difference'] = comparison['difference'].abs()
comparison['pct_difference'] = (
    (comparison['difference'] / comparison['source1_revenue'].replace(0, np.nan)) * 100
).fillna(0)

# Sort by date
comparison = comparison.sort_values('date')

print(f"\n🔍 Comparison Summary:")
print(f"  Total periods compared: {len(comparison)}")
print(f"  Perfect matches: {(comparison['difference'] == 0).sum()}")
print(f"  Discrepancies: {(comparison['difference'] != 0).sum()}")

Step 5: Analyze Discrepancies

def analyze_discrepancies(comparison, threshold_pct=2.0):
    """Identify and categorize discrepancies"""
    
    # Categorize by severity
    comparison['status'] = 'MATCH'
    comparison.loc[comparison['abs_difference'] > 0, 'status'] = 'MINOR'
    comparison.loc[comparison['pct_difference'].abs() > threshold_pct, 'status'] = 'SIGNIFICANT'
    
    # Statistics
    stats = {
        'total_source1': comparison['source1_revenue'].sum(),
        'total_source2': comparison['source2_revenue'].sum(),
        'total_difference': comparison['difference'].sum(),
        'total_pct_diff': (comparison['difference'].sum() / 
                          comparison['source1_revenue'].sum() * 100),
        'periods_matched': (comparison['status'] == 'MATCH').sum(),
        'periods_minor': (comparison['status'] == 'MINOR').sum(),
        'periods_significant': (comparison['status'] == 'SIGNIFICANT').sum(),
        'max_abs_diff': comparison['abs_difference'].max(),
        'avg_abs_diff': comparison['abs_difference'].mean()
    }
    
    return stats

stats = analyze_discrepancies(comparison, threshold_pct=2.0)

print(f"\n📊 Reconciliation Statistics:")
print(f"  Source 1 Total: ${stats['total_source1']:,.2f}")
print(f"  Source 2 Total: ${stats['total_source2']:,.2f}")
print(f"  Difference: ${stats['total_difference']:,.2f} ({stats['total_pct_diff']:.2f}%)")
print(f"\n  Perfect Matches: {stats['periods_matched']}")
print(f"  Minor Variances: {stats['periods_minor']}")
print(f"  Significant Variances: {stats['periods_significant']}")

Step 6: Investigate Root Causes

# Find the worst discrepancies
worst_discrepancies = comparison.nlargest(10, 'abs_difference')

print(f"\n🔍 Top 10 Largest Discrepancies:")
for _, row in worst_discrepancies.iterrows():
    print(f"\n  Date: {row['date'].strftime('%Y-%m-%d')}")
    print(f"    Source 1: ${row['source1_revenue']:,.2f}")
    print(f"    Source 2: ${row['source2_revenue']:,.2f}")
    print(f"    Difference: ${row['difference']:,.2f} ({row['pct_difference']:.1f}%)")

# Investigate patterns
print(f"\n📈 Patterns:")

# Check if discrepancy trends over time
comparison['month'] = pd.to_datetime(comparison['date']).dt.to_period('M')
monthly_variance = comparison.groupby('month')['pct_difference'].mean()

improving = monthly_variance.iloc[-3:].mean() < monthly_variance.iloc[:3].mean()
print(f"  Variance trend: {'Improving' if improving else 'Worsening'}")

# Check for systematic bias
bias = "Source 1 consistently higher" if stats['total_difference'] > 0 else "Source 2 consistently higher"
print(f"  Systematic bias: {bias}")

# Check for specific days of week
comparison['day_of_week'] = pd.to_datetime(comparison['date']).dt.day_name()
dow_variance = comparison.groupby('day_of_week')['abs_difference'].mean()
worst_day = dow_variance.idxmax()
print(f"  Worst day of week: {worst_day}")

Step 7: Drill Down on Specific Discrepancies

def investigate_specific_date(date, source1_df, source2_df):
    """Drill into a specific date's discrepancy"""
    
    # Filter to that date
    s1_detail = source1_df[source1_df['date'] == date]
    s2_detail = source2_df[source2_df['date'] == date]
    
    print(f"\n🔬 Detailed Investigation: {date}")
    print(f"\n  Source 1:")
    print(f"    Records: {len(s1_detail)}")
    print(f"    Total: ${s1_detail['revenue'].sum():,.2f}")
    print(f"    Sample transactions:")
    print(s1_detail[['transaction_id', 'revenue', 'status']].head())
    
    print(f"\n  Source 2:")
    print(f"    Records: {len(s2_detail)}")
    print(f"    Total: ${s2_detail['revenue'].sum():,.2f}")
    print(f"    Sample transactions:")
    print(s2_detail[['transaction_id', 'revenue', 'status']].head())
    
    # Find missing transactions
    s1_ids = set(s1_detail['transaction_id'])
    s2_ids = set(s2_detail['transaction_id'])
    
    missing_in_s2 = s1_ids - s2_ids
    missing_in_s1 = s2_ids - s1_ids
    
    if missing_in_s2:
        print(f"\n  ⚠️  In Source 1 but not Source 2: {len(missing_in_s2)} transactions")
        print(f"    Total value: ${s1_detail[s1_detail['transaction_id'].isin(missing_in_s2)]['revenue'].sum():,.2f}")
    
    if missing_in_s1:
        print(f"\n  ⚠️  In Source 2 but not Source 1: {len(missing_in_s1)} transactions")
        print(f"    Total value: ${s2_detail[s2_detail['transaction_id'].isin(missing_in_s1)]['revenue'].sum():,.2f}")

# Investigate worst discrepancy
worst_date = worst_discrepancies.iloc[0]['date']
investigate_specific_date(worst_date, source1_df, source2_df)

Step 8: Generate Reconciliation Report

def generate_reconciliation_report(comparison, stats):
    """Create comprehensive reconciliation report"""
    
    report = []
    report.append("=" * 60)
    report.append("METRIC RECONCILIATION REPORT")
    report.append("=" * 60)
    report.append(f"\nGenerated: {datetime.now().strftime('%Y-%m-%d %H:%M:%S')}")
    report.append(f"Period: {comparison['date'].min()} to {comparison['date'].max()}")
    report.append(f"\n{'Source 1':20} ${stats['total_source1']:>15,.2f}")
    report.append(f"{'Source 2':20} ${stats['total_source2']:>15,.2f}")
    report.append(f"{'-'*40}")
    report.append(f"{'Difference':20} ${stats['total_difference']:>15,.2f}")
    report.append(f"{'Variance %':20} {stats['total_pct_diff']:>14.2f}%")
    
    report.append(f"\n{'='*60}")
    report.append("SUMMARY")
    report.append("=" * 60)
    report.append(f"  Perfect Matches: {stats['periods_matched']}")
    report.append(f"  Minor Variances: {stats['periods_minor']}")
    report.append(f"  Significant Variances: {stats['periods_significant']}")
    report.append(f"  Average Daily Variance: ${stats['avg_abs_diff']:,.2f}")
    report.append(f"  Maximum Daily Variance: ${stats['max_abs_diff']:,.2f}")
    
    report.append(f"\n{'='*60}")
    report.append("TOP DISCREPANCIES")
    report.append("=" * 60)
    
    top_10 = comparison.nlargest(10, 'abs_difference')
    for i, row in top_10.iterrows():
        report.append(f"\n{row['date'].strftime('%Y-%m-%d')}:")
        report.append(f"  Source 1: ${row['source1_revenue']:>12,.2f}")
        report.append(f"  Source 2: ${row['source2_revenue']:>12,.2f}")
        report.append(f"  Diff: ${row['difference']:>12,.2f} ({row['pct_difference']:>6.1f}%)")
    
    return "\n".join(report)

report = generate_reconciliation_report(comparison, stats)
print(report)

# Save report
with open('reconciliation_report.txt', 'w') as f:
    f.write(report)

# Save detailed comparison to CSV
comparison.to_csv('detailed_comparison.csv', index=False)

Context Validation

Before proceeding, verify:

• Have access to data from all sources being compared
• Metric definitions are clear and documented
• Know what variance is acceptable vs concerning
• Time periods align between sources
• Have unique identifiers to match records (if doing detailed reconciliation)

Output Template

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
METRIC RECONCILIATION REPORT
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Metric: Total Revenue
Period: 2024-12-01 to 2024-12-31
Generated: 2025-01-11 15:30:00

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
SUMMARY
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Production DB        $1,234,567.89
Analytics DW         $1,229,123.45
────────────────────────────────
Difference           $    5,444.44
Variance %                  0.44%

Status: ✅ WITHIN THRESHOLD (< 2%)

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
BREAKDOWN
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Total Days Compared: 31
  ✅ Perfect Matches: 23 days (74%)
  ⚠️  Minor Variances: 6 days (19%)
  🔴 Significant Variances: 2 days (7%)

Average Daily Variance: $175.63
Maximum Daily Variance: $2,345.67

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
TOP 5 DISCREPANCIES
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

1. 2024-12-15
   Production: $45,678.90
   Analytics:  $43,333.23
   Difference: $2,345.67 (5.1%)
   
2. 2024-12-22
   Production: $38,901.23
   Analytics:  $37,123.45
   Difference: $1,777.78 (4.6%)

[... continues ...]

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ROOT CAUSE ANALYSIS
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Pattern: Source 1 consistently higher
Likely Causes:
1. Timing: Production DB updated real-time,
   Analytics DW has 2-hour delay
2. Refunds: Production includes, Analytics excludes
3. Missing Data: 15 transactions on 2024-12-15
   present in Production but not in Analytics

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
RECOMMENDATIONS
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IMMEDIATE:
1. Investigate 2024-12-15 missing transactions
2. Document refund handling difference

ONGOING:
3. Set up daily reconciliation alerts
4. Standardize metric definitions across systems

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
FILES GENERATED
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

✓ reconciliation_report.txt
✓ detailed_comparison.csv (daily breakdown)
✓ discrepancies_only.csv (issues for investigation)

Common Scenarios

Scenario 1: "Daily revenue doesn't match between systems"

→ Compare aggregated daily revenue → Identify which days have discrepancies → Drill into specific days to find missing/extra transactions → Document known timing differences

Scenario 2: "Migration validation - old system vs new system"

→ Compare same metric across systems for overlapping period → Match by transaction ID to find missing/changed records → Validate calculation logic produces same results → Create mapping for known differences

Scenario 3: "Financial reconciliation for month-end close"

→ Compare general ledger to data warehouse → Strict threshold (< 0.1% variance) → Investigate every discrepancy → Produce audit trail documentation

Scenario 4: "Why does dashboard show different number than report?"

→ Compare underlying queries from each → Identify filter differences, timing differences → Document which number is "correct" and why → Fix or annotate the incorrect source

Scenario 5: "Quarterly business review - validate all KPIs"

→ Reconcile multiple metrics systematically → Create reconciliation matrix (metric × source) → Flag metrics that need definition alignment → Prioritize fixes by business impact

Handling Missing Context

User says "numbers don't match" without specifics: "Let me help reconcile. I need:

1. What's the metric? (revenue, user count, etc.)
2. What are the two numbers you're seeing?
3. Where is each number coming from? (system, report, dashboard)
4. What time period?"

User doesn't know metric definitions: "No problem. I'll extract the underlying queries/data from each source and reverse-engineer how they're calculating the metric. Then we can see where they diverge."

User doesn't have direct data access: "Can you export the data to CSV from each source? Or screenshot the summary numbers? I can work with whatever you have access to."

No transaction-level data available: "We'll do aggregate comparison only. This will show the magnitude of the difference but won't pinpoint specific missing transactions."

Advanced Options

After basic reconciliation, offer:

Automated Monitoring: "Want me to create a script that runs this reconciliation daily and alerts you when variance exceeds threshold?"

Multi-Source Reconciliation: "If you have 3+ sources to compare, I can create a reconciliation matrix showing all pairwise comparisons."

Trend Analysis: "I can track reconciliation over time to show if data quality is improving or degrading."

Root Cause Classification: "I can categorize discrepancies by likely cause (timing lag, missing data, calculation difference, etc.) to prioritize fixes."

Documentation Generation: "I can create formal documentation of known differences between sources for your team's reference."