Business – 8.1 Marketing analysis – Sales forecasting | e-Consult

Step 1 – Compute the ratio of actual sales to the centred moving average for each month where a centred MA exists (Months 2‑7):

Step 2 – Allocate each ratio to its seasonal position (Month 1‑4 repeat). Assuming the data start at Month 1, the mapping is:

• Month 2 → Seasonal position 2
• Month 3 → Seasonal position 3
• Month 4 → Seasonal position 4
• Month 5 → Seasonal position 1
• Month 6 → Seasonal position 2
• Month 7 → Seasonal position 3

Step 3 – Average the ratios for each seasonal position:

Step 4 – Normalise so that the sum of the four indices equals 4 (average = 1):

Current sum = 0.877 + 0.989 + 0.923 + 1.007 = 3.796.

Adjustment factor = 4 / 3.796 = 1.054.

Final seasonal indices:

• Month 1: 0.877 × 1.054 ≈ 0.925
• Month 2: 0.989 × 1.054 ≈ 1.043
• Month 3: 0.923 × 1.054 ≈ 0.973
• Month 4: 1.007 × 1.054 ≈ 1.061

These indices will be used to deseasonalise and to produce forecasts.