In preparing this Outlook, the influence the overall size and growth rate of the relationships were carefully examined among economy, which, in turn, determines the level energy production, consumption and prices, as and composition of energy supply and demand. [...] The productivity per worker is The population projection is consistent with the projected to increase at an average annual rate of declining trend in fertility, with immigration 1.6 percent over the projection, compared with a assumed to remain unchanged at about 225,000 historical value of 1.4 percent for the period immigrants per year, and net immigration of 1990-2004 (Table M2). [...] This translates into an average growth expected trends in the formation of households rate of 0.8 percent in employment as the to arrive at the number of households, which is unemployment rate is assumed to fall to 6.6 one of the main determinants of energy use in percent by the year 2020. [...] The Reference Case 2006 7 Key Drivers for Energy The combination of productivity growth and COMPOSITION OF THE ECONOMY labour force growth leads to an anticipated increase of 2.4 percent per year in economic The composition3 of the economy is expected to activity, measured in terms of constant-dollar (or change somewhat over the course of the outlook real) Gross Domestic Product (GDP) over the as [...] This projected The price of natural gas is driven in part by the decline will be primarily a result of the similar price of crude oil, by the characteristics of the decline in the crude oil price.