Cash flow is defined as (operating income before depreciation,
income taxes and interests) less (interest payments)
less (income taxes). This definition is quite similar to (net
income) plus (depreciation). It was selected over the latter
definition because less ambiguity from alternative accounting
procedures arises. It was assumed that the impact of cash
flow in several previous periods influences R&D expenditures
in the current period. The motivating assumption is that the
capital budgeting process is one whereby funds allocated to
R&D vary according to the firm's cash position (assuming
that the internal cost of capital is below the external cost of
capital). Hence investment decisions which could be justified
only on the basis of the lower internal cost of funds will be
postponed or abandoned when the firm's cash position is less
liquid. A lag effect over several years was assumed because
the capital budgeting decision takes time and because sustained
changes in the firm's cash positions have more effect
than one year fluctuations.