We justify the last assumption on the grounds that future changes in cell phone energy require- ments depend largely on changes in user habits and changes in manufacturing efficiency. Thus they are difficult to predict. However, we drop this assumption in our final sectio Energy Consumption Model Our approach involves three steps: We model households as state machines with various phones and appliances We use demographic data to determine the probability of households changing state. By simulating multiple households, we extrapolate national energy impacts Households The ributes: nt of our model is the household. each household has the follo attr m: A number of members old enough to need a telephone. t: A number of landline telephone c: A number of members with cellular phones The state of each household can be described in terms the above values. We will generate m from available demographic data and hold it constant A household can exist in one of four disjoint states at a time. Each state has two associated conditions Initial State-When a household only uses landline telephones 0 Acquisition State- After a household acquires its first cell phone 0<c< Transition State- After all household members have their own cell phone but the landline t>0 The UMAP Journal 30(3)(2009). @Copyright 2009 by COMAP, Inc. All rights reservedWe justify the last assumption on the grounds that future changes in cell phone energy require￾ments depend largely on changes in user habits and changes in manufacturing efficiency. Thus, they are difficult to predict. However, we drop this assumption in our final section. Energy Consumption Model Our approach involves three steps: • We model households as state machines with various phones and appliances. • We use demographic data to determine the probability of households changing state. • By simulating multiple households, we extrapolate national energy impacts. Households The basic component of our model is the household. Each household has the following attributes: • m : A number of members old enough to need a telephone. • t : A number of landline telephones. • c : A number of members with cellular phones. The state of each household can be described in terms the above values. We will generate m from available demographic data and hold it constant. A household can exist in one of four disjoint states at a time. Each state has two associated conditions. • Initial State - When a household only uses landline telephones. • t > 0 • c = 0 • Acquisition State - After a household acquires its first cell phone. • t > 0 • 0 <c < m • Transition State - After all household members have their own cell phone but the landline is retained. • t > 0 • c = m The UMAP Journal 30 (3) (2009). ©Copyright 2009 by COMAP, Inc. All rights reserved