The details of clock sales at a supermarket for the past 6 weeks are shown in the table below. The time series appears to be relatively stable, without trend, seasonal, or cyclical effects. The simple moving average value of k is set at 2. Week Units Sold 2-period Moving Average Error Absolute Error 1 15 N/A 2 18 N/A 3 13 16.5 -3.50 3.50 4 16 15.5 ? 0.5 5 15 14.5 95 0.5 0.5 6 MAD What is the error for week 4? 15.5 01 -0.5 0.5