(Hamilton, Nickerson, et al. 2003). Data from a large group incentive scheme at Continental Airlines even found positive effects in the presence of strong free-rider incentives (Knez and Simester 2001).

# **Experimental studies**

Among experimental studies a distinction has to be made between laboratory and field experiments, with each having their own advantages and disadvantages. Laboratory experiments are characterized by their strong control over experimental design and treatment specification, but often lack the ability to use representative subjects or simulate convincingly real-world settings. Field experiments combine the randomized assignment of treatment with actual real-world programs and participants, but are often more constrained in their design choices, face stronger exogenous pressures to succeed and are resourceintensive.

# **_Meta-studies_**

(Jenkins, Mitra, et al. 1998) provided the first meta-analysis of the psychological literature on the impact of financial incentives on performance and concluded, based on analysis of 47 studies that these incentives resulted in a 12% improvement in performance quantity and a negligible effect on performance quality. The study however had several limitations as it did not distinguish between types of incentive programs, complexity of tasks, and differences in organizational settings.

Building on the Jenkins study, (Condley, Clark, et al. 2003) conducted a meta-analysis of 64 field and laboratory experiments, as well as observational studies, on the impact of monetary and non-monetary individual and group incentives on performance. The criteria for inclusion of studies in the analysis was that studies had to (a) have a use a control group or a pre-treatment measure of average performance; (b) involve the use of incentives to enhance performance; and (c) and report some statistical data. The studies included private sector settings, public sector, as well as laboratory experiments with college students. Within the public sector, however the vast majority were of schools, with only one study in a core government setting, thereby greatly limiting the generalizability of the findings to the core civil service. Importantly, the analysis also distinguished between studies that looked at cognitive (38 studies) versus mechanical manual tasks (26 studies), and the measurability of the tasks, looking at both quantitative and qualitative performance targets. The results of the meta-analysis showed that employees and other research participants who received performance incentives achieved an average 22% increase in work performance. The findings were irrespective of the settings, although again it should be noted that there was only one study of performance incentive in a government agency. Monetary incentives were found to be more effective than non-monetary gifts, and group-based incentives were significantly more effective (48% increase in performance) than individual incentives (19% increase). While the incentives worked for both cognitive and physical tasks, the gains were higher for the latter (30% increase compared to 20% increase). No significant difference was found based on the measurability of the tasks.

(Weibel, Rost, et al. 2009) conduct a meta analysis of 46 high quality empirical studies published in the fields of economics and psychology and covering both simple and complex tasks, and with both quantitative and qualitative outcome measurements. Overall the study finds a statistically significant and positive effect of pay for performance on performance; however, and in contrast to the above, the findings were significantly positive for simple tasks and smaller, but still statistically significant, negative effect for complex tasks. The authors argue that this negative effect is due to the reduction in intrinsic motivation brought about by the incentive scheme.

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