Data Cleaning

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Best Practices for Data Cleaning

Here are some key guidelines to follow when cleaning your data:

1. Document All Changes

• Keep a detailed log of all modifications made to the dataset.
• Store this documentation alongside the data for transparency and reproducibility.
• Documenting your cleaning steps is not optional — it’s what separates scientific work from data dredging. Without clear records, your analysis becomes difficult to verify, reproduce, or trust.

2. Understand the Data

• Review the data description and metadata to ensure consistency.
• Verify that the data complies with relevant regulations (e.g., GDPR).

3. Handle Missing Values Carefully

• Identify how missing values are encoded (e.g., NA, -999, "I don't know", "Prefer not to answer").
• Distinguish between different types of missingness (e.g., refusal to answer vs. lack of knowledge).
• Decide on appropriate strategies: imputation, removal, or flagging.

4. Check Data Structure

• Ensure that each row represents an observation and each column a variable.
• Column names should be on a single line and clearly labeled.
• Remove empty columns and lines unless justified.

5. Verify Data Types

• Each column should contain a single, consistent data type (e.g., numeric, categorical, date).
• Convert or correct types as needed (e.g., strings to dates, floats to integers).

6. Validate Data Integrity

• After importing/exporting data, check that the number of rows and columns remains unchanged.
• Compare summary statistics before and after transformations.

7. Explore Numerical Variables

• Use descriptive statistics (min, max, mean, quantiles) and visualizations (boxplots, histograms).
• Identify outliers or impossible values (e.g., negative heart rate).

8. Review Categorical Variables

• Check for inconsistent labels (e.g., "Belgium" vs. "belgium").
• Standardize categories and remove duplicates or typos.

9. Detect Duplicates

• Look for and remove duplicate rows or records unless justified.

10. Ensure Logical Consistency

• Cross-check related variables for contradictions (e.g., Marital Status = Single but Spouse Name is filled).
• Use validation rules to flag inconsistencies.