Seasonal indices by the average percentage method, deseasonalising and predicting from the trend line

What this note covers

1. What a seasonal index is
2. The average percentage method, step by step
3. Worked example: four quarterly indices
4. The sum check, and what to do if it fails
5. Deseasonalising a time series
6. Fitting the trend line to deseasonalised data
7. Predicting and reseasonalising
8. How this is examined in the WACE ATAR course examination

8 sections · 12 key terms & formulas · 6 common mistakes