this increase in discovered cartels could also result from a rising number of active price-fixing agreements, suggesting that cartels are not impressed by recent adjustments in European competition law and that the aim of optimal deterrence is still not achieved.
Regarding different antitrust law regimes, the results contradict expectations. Al- though periods 2, 4 and 5 show negative signs, the estimated coecients are not statistically significant. Thus, more severe antitrust regulations do not seem to lead to reservation in the price-setting behavior of cartels. This finding is surprising and indicates that cartels acting in Europe are not deterred by recent adjustments of national and pan-European antitrust laws. However, as mentioned before one could also argue that exactly these fine adjustments in preceding years encouraged cartel participants to increase their overcharge level. As the fine level becomes higher some firms might decide to either reject collusion at all (optimal deterrence) or to start collusion and demand exorbitant overcharges in order to outweigh expected punishments. Following the latter reasoning as well and taking both arguments together, the insignifi- cant changes in the overcharge level during the five antitrust law periods are not unexpected. Nevertheless, one should keep in mind that the change in the magnitude of overcharges is only one indicator for deterrent effects of antitrust law adjustments. Other factors such as cartel stability in terms of cartel duration, number of repeated at- tempts to collude or internal uncertainties due to leniency programs must be taken in to account as well. In this context it is worth noting that both cartel duration and repeated attempts to collude decreased noticeably in the latest two antitrust law periods, indicating destabilization and deterrent effects of antitrust law changes over time.