The Vortex of Social Structure and Social Movements: A Prey-Predator Model of Trade Unions and Inequality in Capitalist Countries (1870-2013)

This submission shows that – in the long historical run – trade unions and income inequality influence each other according to a prey and predator model, as initially developed by Lotka and Voltera (1925). A strong negative correlation between inequality and union density has long been noticed, but regressions are insufficient to understand the dynamic non-linear relation between trade union membership and income inequality.

We therefore underline the historical existence of a lag of about one decade between inequality (measured by the Gini index, or the share of the upper decile of incomes) and social mobilization (union density). We show that increases in inequality augment trade union membership with a lag of several years. In turn, trade union membership decreases inequality after several years. But later low inequality means that trade unions encounter increasing difficulties in recruiting new members. This leads to low trade union membership as a long-term result of decreased inequality. With few trade union members, the balance of power becomes less favorable for the remaining trade union members that favor less inequality, and thus inequality increases again. When inequality is high, the circle starts again as trade unions – after some time lag – recruit new members as a result of higher inequality.

Using data that was just recently made available on trade union membership (Tilly 2000; Crouch 1993; Visser 2013) and income inequality (Alvaredo, Atkinson, Piketty, Saez 2013) over the last 140 years, this model explains trade union membership and income inequality as mutually causing each other in Canada, Italy, Germany, France, the UK and the US. Using a structural equation model, we show the parameters according to which income inequality and trade union membership interact in a perpetually instable equilibrium over time. This structural equation model works better than simple correlations or regressions, by making it possible to see trade union membership and inequality both as dependent and independent variable, thus offering a non-linear relationship of mutual influence between trade union membership and inequality. The two time lags we detect, the first between the reality of inequality and its consequences in terms of collective action, and the second between trade union development and inequality reduction, have an important role in these dynamics. The delays that exist in both mean that societies’ reactions to new realities are delayed, and that social realities in turn change slowly when new balances of political power arise.

This dynamic is essential to understand the socio-economic non-linear long-wave dynamics of the 20^th, and possibly also of the 21^st century. This is because inequality is currently on the rise and might continue to increase, as long as no strong collective action is launched by trade unions or other actors, but using historical data, we can show that social movements that fight inequality have always reacted with latency to increased inequality as we witness today.