About Our Data

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The Dataset

Source

• Official DVSA MOT History Data (publicly available via DVSA API)
• Period Analyzed: January 2024
• Total Tests: 62,898
• Unique Vehicles: 51,593
• Geographic Coverage: All UK postcode areas

What We Have

✅ Test date, result, mileage, vehicle age
✅ Make, model, fuel type, engine capacity
✅ Test type (initial vs retest)
✅ Postcode area (anonymized for privacy)

What We Don't Have

❌ Specific failure reasons (not included in this dataset)
❌ Advisory details
❌ Individual vehicle identifiers
❌ Owner information

Important: Our analyses focus on pass/fail patterns, mileage norms, and retest rates. We cannot analyze specific component failures with this dataset.

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Data Quality

Completeness

• 99.1% complete across all critical fields
• Missing mileage: 551 records (0.9%)
• Missing engine capacity: 244 records (0.4%)
• Zero date parsing errors

Validation

Every record passes through:

1. Schema validation (Pydantic models enforce data types)
2. Range checks (e.g., mileage 0-500,000, age 0-50 years)
3. Consistency checks (test date > first use date)

Records failing validation are excluded from analysis (< 0.1% of raw data).

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Methodology

How We Calculate Pass Rates

Pass Rate = (Tests with result 'P' or 'PRS') / Total Tests × 100

• P = Passed
• PRS = Passed after rectification at station
• F = Failed
• ABA/ABR = Aborted (excluded from pass rate calculations)

Sample Size Confidence

We apply strict thresholds for publishing statistics:

Sample Size	Confidence	We Publish?
< 50 tests	Low	❌ No
50-500 tests	Medium	⚠️ With caveat
500+ tests	High	✅ Yes
2,000+ tests	Very High	✅ Yes, featured

Example: Our Ford Focus guide is based on 7,616 tests - very high confidence.

Age Cohorts

Vehicles are grouped by age at time of MOT test:

• 0-2 years: Nearly new
• 3-5 years: Early maturity
• 6-9 years: Mid-life
• 10+ years: Veteran

Pass rates are calculated separately for each cohort.

Mileage Benchmarks

For each model/age combination, we report:

• Median: 50th percentile (typical)
• IQR: 25th-75th percentile range
• 90th percentile: High mileage threshold

This allows you to see where a specific car sits relative to its peers.

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Limitations & Caveats

1. Single-Month Snapshot

Our current analysis covers January 2024 only. This is a limitation. Seasonal patterns may exist (e.g., more retests after winter salt corrosion).

Mitigation: We will expand to full-year 2024 data when available and update all statistics.

2. Selection Bias

MOT tests are required at 3 years, then annually. Newer cars (<3 years) are not represented. Our data skews towards older vehicles.

3. Geographic Variance

Postcode-level pass rates may be influenced by:

• Local testing standards (we assume consistency, but cannot verify)
• Environmental factors (coastal corrosion, urban pollution)
• Socioeconomic patterns affecting maintenance

We report geographic trends but urge caution in interpreting causality.

4. No Causal Inference

Correlation ≠ Causation. If Model A has a higher pass rate than Model B, we cannot definitively say Model A is "better engineered." It could reflect owner demographics, maintenance habits, or usage patterns.

We present data; we invite you to draw informed conclusions.

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For Researchers & Data Journalists

Reproducibility

All our visualizations and statistics are generated from code. Our process:

1. Raw data ingestion (data_ingest.py)
2. Cleaning & validation (clean_transform.py)
3. Feature engineering (features.py)
4. Statistical analysis (analytics.py)
5. Visualization (viz.py)

Code: Available on request for verification purposes.

Downloadable Data

In the spirit of transparency, we offer our aggregated, anonymized dataset for download:

What's included:

• Pass rate by make/model/age cohort
• Median/IQR mileage by make/model/age
• Retest rates
• Sample sizes for confidence assessment

What's NOT included:

• Individual vehicle identifiers
• Registration numbers
• Owner information
• Postcode-level data

Citation

If you use our data or insights, please cite:

CompareMOTHistory.com (2025). UK MOT Pass Rates Analysis: January 2024 Dataset. Retrieved from https://comparemothistory.com/about-data/

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Our Commitment

We will:

• ✅ Update this page when we analyze additional data
• ✅ Correct errors if found (with public changelog)
• ✅ Acknowledge limitations rather than hide them
• ✅ Respond to methodology questions via [email protected]

We won't:

• ❌ Invent or extrapolate data
• ❌ Cherry-pick statistics to support narratives
• ❌ Hide sample sizes or confidence levels
• ❌ Make causal claims without evidence

The Honest Mechanic doesn't just show you the data - we show you how we got it.

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Questions?

Technical questions: [email protected]
Data requests: [email protected]
Press inquiries: [email protected]

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