Relations between business margins and structural variables including buyer and seller concentrations have been examined using data on strategic business units in the PIMS data base. The results are compared with earlier work based on industry classified data. It is now possible to identify whether the observed changes in margin are due to direct effects on profit or to changes in the fixed costs included in gross margins. New data are presented on the role of capacity utilisation in relation to the balance of buyer and seller power and on changes in margin through the life cycle.

This study examines day-of-the-week effects using hourly values of the Dow Jones Industrial Average. We find that over the 1963–1983 period the weekend effect has sifted from characterizing active trading on Monday to characterizing the non-trading weekend. Over the early part of our sample period negative returns characterize each hour of trading on Monday, while the return from Friday close to Monday open is positive. In the most recent subperiod, Monday average hourly returns after noon are all positive and the weekend effect is due to negative average returns from Friday close to Monday open.