40. Electricity Consumption Using Deseasonalization. Electric power consumption is measured in kilowatt-hours (kWh). The local utility company offers an interrupt program whereby commercial customers that participate receive favorable rates but must agree to cut back consumption if the utility requests them to do so. Timko Products cut back consumption at 12:00 noon Thursday. To assess the savings, the utility must estimate Timko’s usage without the interrupt. The period of interrupted service was from noon to 8:00 p.m.

Data on electric power consumption for the previous 72 hours are available.

Time Period Monday Tuesday Wednesday Thursday 12–4 a.m. — 19,281 31,209 27,330 4–8 a.m. — 33,195 37,014 32,715 8–12 noon — 99,516 119,968 152,465 12–4 p.m. 124,299 123,666 156,033 4–8 p.m. 113,545 111,717 128,889 8–12 midnight 41,300 48,112 73,923

a. Is there a seasonal effect over the 24-hour period?

b. Compute seasonal indexes for the six 4-hour periods.

c. Use trend adjusted for seasonal indexes to estimate Timko’s normal usage over the period of interrupted service.