On the Determinants of Investment

It is well known that an economy’s output levels and employment levels are determined by the level of investment. The popular story presented in mainstream textbooks and taught in conventional courses is that of planned saving adapting to planned investment, with the rate of interest as the equilibrating factor. This is the supply-side vision of the economy wherein demand can never be a constraint except temporarily due to frictions or imperfections. Additionally, this view reaches the conclusion that that there is a tendency to full-employment in capitalist economies. This blog post revisits the saving-investment relationship, the investment function and the link between the rate of interest and investment. Given the crucial role investment plays in an economy, it is important that we critically appraise its determinants.

By investment, economists mean the purchase of capital goods and not financial assets. Saving refers to the income that is not consumed. Saving is a leakage from the economy while investment is an injection. Marginalist (neoclassical) economics maintains that planned saving and planned investment are equilibrated through variations in the rate of interest which is assumed to be sufficiently sensitive to any saving-investment disequilibrium. Planned saving is a positive function of the rate of interest while planned investment is a negative function of the rate of interest. When planned saving is in excess of planned investment, there is excess savings which puts a downward pressure on the rate of interest and vice versa. However, is such an a priori functional link between the rate of interest and the rate of accumulation a correct one? The 1960s capital theory debate demonstrates the implausibility of an interest-elastic investment function on logical grounds. Also, in a world where the rate of interest is set by monetary policy (and therefore exogenous to the saving-investment process) it is unclear how it can play the role of an equilibrating force as suggested by marginalist economics.

The non-orthodox approach to activity levels and growth draws inspiration from the principle of effective demand of Kalecki and Keynes. The investment function is not interest-elastic in this theoretical approach, also called the demand-led approach. Here, investment depends on ‘the future expected level of effective demand (D+1), which tells us how much capacity firms will need, and on the current technical conditions of production (represented in this simple model by the normal capital-output ratio)…’ (Serrano 1995: 78; available freely here). In this simple model, note that production is assumed to be carried out with circulating capital only. So, I = aD+1 where a is the capital-output ratio. A change in technology will affect the capital-output ratio, which indicates how much of capital is required to produce one unit of output. Further, we make the realistic assumption that firms do not systematically err in their expectations. The expectations of firms of course depend on policy certainty. Policy uncertainty affects consumption and investment decisions in an adverse manner.

As a matter of fact, a recent IMF working paper on the situation of India provides partial support to the demand-led approach. They note: ‘Real interest rates account for only one quarter of the explained investment slowdown.’ For them, the key factor is policy uncertainty, but, the demand-led growth theorists, I think, will advocate the examination of the exact mechanisms through which monetary and/or fiscal policies have deterred investment. Without explaining further in this blog post, the answer might be found in the manner in which autonomous elements of demand such as autonomous consumption, research & development expenditures, government expenditures and foreign expenditures are affected by policy uncertainty. To conclude, it is time that the interest-elastic investment function is seriously questioned both on theoretical and empirical grounds, and subsequently discarded.