Firm Heterogeneity and the Aggregate Labour Share

Using a static model of firm behaviour with imperfect competition on the product and labour markets, we quantify the effect of firm heterogeneity in total factor productivity, product and labour market power, wages and output prices on the aggregate labour share. In particular, we suggest a new decomposition of the aggregate labour share in terms of the first moments of the joint distribution of these variables across firms, providing a bridge between the micro and the macro approach to functional distribution. We provide an application of our method to the UK manufacturing sector, using firm-level data for the period 1998-2014. The analysis confirms that heterogeneity matters: in an economy populated only by representative firms, the labour share would be 10 percentage points lower. However, and contrary to a common narrative focussing on increasing disparities between firms, the observed decline in the aggregate labour share over the period is driven entirely by the decline in the labour share of the representative firm, mostly due to an increasing disconnect between average productivity and real wages. Changes in the dispersion of firm-level variables have contributed to slightly contain this decline