Data Transformations Reference
Quick reference guide for all available FRED data transformations.Transformation Codes
| Code | Name | Formula | Use Case |
|---|---|---|---|
| lin | Levels | x_t | Raw values |
| chg | Change | x_t - x_ | Period change |
| ch1 | Change YoY | x_t - x_ | Annual change |
| pch | % Change | ((x_t/x_)-1)*100 | Growth rate |
| pc1 | % Change YoY | ((x_t/x_)-1)*100 | Annual growth |
| pca | Annual Rate | (((x_t/x_)^n)-1)*100 | Annualized |
| cch | Log Change | (ln(x_t)-ln(x_))*100 | Log returns |
| cca | Log Annual | (ln(x_t)-ln(x_))*100 | Annual log |
| log | Natural Log | ln(x_t) | Log levels |
Selection Guide
By Data Type
Flow Variables (rates, prices):- Use: pch, pc1, pca
- Example: Inflation, interest rates
- Use: chg, ch1
- Example: Employment, inventories
- Use: cch, log
- Example: Stock prices, exchange rates
Common Mistakes
❌ Don’t:- Transform already-transformed series
- Mix frequencies when comparing
- Ignore seasonal adjustment
- Check original units
- Use consistent transformations
- Document your choices