Having thought about this relationship a little more, this seems to nicely tie into the two regimes of CasP: breadth & depth.
During a breadth regime (booms in corporate amalgamation), capitalist accumulation takes on a much different form than during depth (lulls in amalgamation and resort to inflation).
My understanding of Nitzan and Bichler's theory is that breadth is a capitalist vs capitalist struggle, while depth is capitalist vs. workers struggle. During the former regime, it would seem that capitalist class accumulation is amicable to growth and low employment -- the fate of capitalists and workers are linked -- growth seems to make everything better.
However, during a regime shift to depth, suddenly capitalist accumulation is in direct conflict with workers and unemployment actually aids accumulation.
Over the 20th century, profit's share of national income has remained in a tight, negative correlation with unemployment, a tight, positive correlation with the growth of useful work (a biophysical metric that I use extensively in my research). A breadth regime, then, is a general faith in profit -- or as Nitzan & Bichler state --- in the differential rate of return.
During depth regimes, this faith in profit is destroyed, and capitalists flee to the average rate of return (interest baring debt). Capitalist can still accumulate, but the game becomes zero sum (or even negative sum) for society at large. My interpretation, then, is that interest is effectively a hedge against growth. A breadth regime is far preferable to a depth regime (for capitalists and society) but since capital accumulation is an imperative, a hedge (or safe haven) is always wise.
However, when too many capitalists flee to this safe haven, we enter a depth regime.
But how do we account for these regimes oscillations? Is it capitalist class action as a whole, or a smaller capitalist fraction? Or state action? Where does government policy fit in? For instance, the depth regime of the late 70s and early 80s corresponds with both an oil crisis (the OPEC cartel flexing its muscles) and the Volker shock (the Federal reserve hiking interest rates to unheard of levels in order quell inflation).
In my opinion, the empirical evidence seems to show that the relationship between unemployment and capitalist income is neither intuitive nor straightforward.
What would be fantastic would be to get data for both capitalist income and unemployment from a huge cross section of countries. The World Bank is my normal go-to place for such global data; however, to my knowledge it does not collect data on capitalist income.
Does anyone know where such data might be obtained?