Now we need to figure out how production gets determined. Over the long term investment and capacity are clearly important, but these have been extremely stable. In the shorter term more people are hired and, if necessary, an additional production shift added. There is quite a bit of complicated stuff going on when shifts are added: management changes, maintenance scheduling problems arise, and so on. However, as a first approximation, more people make more products, and this is a good starting point, so we add the level Workforce.
The things that change workforce are hiring, layoffs, firings and retirements. Again, for simplicity we combine all of these into a composite concept — the net hire rate. Note that net hire rate can either increase or decrease the workforce.
