Much remains to be done before economists can reach solid conclusions about the impact of innovation investment on productivity. Still, this research has made solid progress. "We see our results as a useful benchmark for future research aimed at developing models of endogenous technical change that are useful for quantitative policy analysis," the economists conclude. According to this benchmark, policies aimed at stimulating firms' investments in innovation are likely to have a modest impact on productivity and living standards over time horizons of a decade or two, but it is possible that such policies could have a dramatic impact on welfare over long horizons if intertemporal knowledge spillovers are large enough.