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Data Quality Dimensions

The 10 Most Common Data Quality Problems and How to Fix Them

Across industries and data types, the same quality problems appear repeatedly. Here are the 10 most common data quality issues, why they happen, and how to fix them systematically.

Key Takeaways
  • Duplicates are the most common and most impactful — implement entry-time prevention before cleanup
  • Missing timestamps (created_at, updated_at) block every freshness and timeliness measurement
  • Free-text fields that should be dropdowns are the root cause of most category inconsistency
  • Foreign key constraints prevent orphaned records — enable them in every production database
  • Self-reported data requires verification at entry to achieve accuracy — collecting it isn't enough

1. Duplicate Records

What: The same entity appears multiple times in a dataset. Why: Multiple data entry points, system migrations, bulk imports without deduplication. Fix: Implement duplicate detection at entry (check for existing email before creating a new record). Run a deduplication project on existing data. Establish a single entry point for master data.

2. Missing Required Values

What: Critical fields are blank for a significant portion of records. Why: Fields weren't required at entry, forms were redesigned without enforcing required fields, data imported from external sources. Fix: Make required fields mandatory in your entry system. Use enrichment services to fill missing values for existing records. Migrate to required-field enforcement.

3. Inconsistent Formatting

What: The same type of value stored in multiple formats (phone numbers, dates, addresses). Why: Multiple entry points with different standards, manual entry without format validation, data from multiple sources. Fix: Adopt international standards (ISO 8601 for dates, E.164 for phones). Enforce format validation at entry. Normalize existing data with a cleanup script.

Sohovi lets you set up validation rules for any column and instantly see which rows fall outside them — no code or SQL required.

4. Stale or Outdated Data

What: Data that was once accurate has decayed — people changed roles, companies changed names, addresses changed. Why: No re-verification process, data captured once and never refreshed. Fix: Implement a re-verification cadence. Add created_at and updated_at timestamps. Use engagement signals (email bounces, returned mail) as passive freshness indicators.

5. Orphaned Records

What: Records that reference deleted parent records (broken foreign keys). Why: Cascading deletes not configured, manual database edits, migration errors. Fix: Enable foreign key constraints. Configure appropriate cascade behavior for each relationship. Run integrity checks after migrations.

6. Inaccurate Self-Reported Data

What: Values entered by users that are incorrect — fake emails, wrong job titles, rounded numbers. Why: No verification at entry, users have incentive to provide inaccurate data. Fix: Verify critical fields at entry (email verification via confirmation, address autocomplete). Cross-reference with authoritative sources for high-value records.

Sohovi scores your dataset against your own accuracy standards and highlights the columns and rows where values fall outside expected ranges.

7. Mixed Data Types

What: A column intended for numbers contains both numbers and text ("N/A", "TBD", "$5,000"). Why: No type enforcement at entry, manual spreadsheet editing. Fix: Enforce column types in database schemas. For spreadsheets, use data validation. During cleanup, categorize non-numeric values as either null (truly missing) or coded values.

8. Poorly Defined Categories

What: Status or category fields with too many values or redundant values ("Active", "active", "Active Customer", "Current"). Why: Free-text fields used where dropdowns should be, no canonical value list. Fix: Define a canonical value list. Convert free-text to a dropdown. Map existing non-standard values to canonical values during a cleanup project.

9. Disconnected Data Across Systems

What: The same entity represented differently in different systems with no shared identifier. Why: No master data management, different systems added organically without integration. Fix: Establish a master identifier in the primary system of record. Sync that ID to all other systems. Define the authoritative system for each attribute.

10. No Data Timestamps

What: Records have no created_at or updated_at fields, making freshness and change tracking impossible. Why: Timestamps weren't included in the original schema design. Fix: Add timestamps to all tables going forward. For existing records, backfill created_at with a reasonable estimate where possible. This is foundational for any data quality monitoring.

Sohovi tracks quality trends across runs and alerts you when a metric — null rate, duplicate count, score — moves outside its normal range.

Frequently Asked Questions

Which of these 10 problems should I fix first?

Start with duplicates and missing timestamps — they have the broadest impact and unblock other quality work. Duplicates inflate every count metric; timestamps enable everything from freshness monitoring to GDPR compliance.

Can I fix all of these without a dedicated data engineering team?

Problems 1–5 are fixable with process changes and basic SQL. Problems 6–10 may require development work (schema changes, validation at entry). Start with process and configuration fixes; escalate to engineering only when necessary.

Which of these is hardest to fix after the fact?

Missing timestamps. Once data is in a system without created_at, you can't recover when it was created — you can only estimate. This is why adding timestamps is the first recommendation for any new data system.

Selva Santosh

Data quality, for people who ship

Selva writes practical guides on data quality, profiling, and governance to help teams ship better data.

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