Facts and figures about UK taxes, benefits and public spending.
Income distribution, poverty and inequality.
Analysing government fiscal forecasts and tax and spending.
Analysis of the fiscal choices an independent Scotland would face.
Case studies that give a flavour of the areas where IFS research has an impact on society.
Reforming the tax system for the 21st century.
A peer-reviewed quarterly journal publishing articles by academics and practitioners.
We consider the estimation of Cobb-Douglas production functions using panel data covering a large sample of companies observed for a small number of time periods. Standard GMM estimators, which eliminate unobserved firm-specific eects by taking first differences, have been found to produce unsatisfactory results in this context (Mairesse and Hall, 1996). We attribute this to weak instruments: the series on rm sales, capital and employment are highly persistent, so that lagged levels are only weakly correlated with subsequent first differences. As shown in Blundell and Bond (1998), this can result in large finite-sample biases when using the standard first-differenced GMM estimator. Blundell and Bond (1998) also show that these biases can be dramatically reduced by exploiting reasonable stationarity restrictions on the initial conditions process. This yields an extended GMM estimator in which lagged first-differences of the series are also used as instruments for the levels equations (cf. Arellano and Bover, 1995). Using data for a panel of R&D-performing US manufacturing companies, similar to that in Mairesse and Hall (1996), we show that the instruments available for the production function in first differences are indeed weak. We find that the additional instruments used in our extended GMM estimator appear to be both valid and informative in this context; this estimator yields much more reasonable parameter estimates. We also stress the importance of allowing for an autoregressive component in the productivity shocks.
View all IFS Working Papers in the series
Recent IFS Working Papers
The UK's public finances in the long run: the IFS model
This working paper describes how the IFS’s model of the UK’s long-run public finances (and those of its constituent nations) is constructed.
Efficient responses to targeted cash transfers
In this paper, we estimate a collective model of household consumption and test the restrictions of collective rationality using z-conditional demands in the context of a large Conditional Cash Transfer programme in rural Mexico.
Policy discontinuity and duration outcomes
A comparison of hazard rates of duration outcomes before and after policy changes is hampered by non-identification if there is unobserved heteogeneity in the effects and no model structure is imposed. We develop a discontinuity approach that overcomes this by exploiting variation in the moment at which different cohorts are exposed to the policy change, i.e. by considering spells crossing the policy change.