Other studies have investigated firm-specific motives for income smoothing from wider, external perspectives. Belkaoui and Picur (1984) draw on theories of economic duality to argue that firms in peripheral sectors have greater incentives to smooth than firms in core sectors. Firms are classified as operating in either core or peripheral sectors on the basis of capital intensity, unionisation, asset size and market characteristics. Their empirical results offer weak support for such an argument, suggesting that firms in peripheral sectors face a more restricted opportunity structure and a higher degree of environmental uncertainty. Craig and Walsh (1989) argue that the higher a firm's potential political costs, earnings variability and market risk, the stronger managers' incentives to smooth income by the use of extraordinary items. Their findings, however, support only the political cost hypothesis.