This article examines the relative contributions of sector allocation and security selection in the context of long-only equity portfolio management. Building upon the fundamental law of active management, we demonstrate that attaining a specified information ratio with lower breadth necessitates a correspondingly higher hit rate, reflecting greater investment skill. For long-only equity managers, allocation decisions, while foundational in establishing a strategic investment framework, require heightened predictive accuracy due to their intrinsically lower breadth. An empirical examination of leading US large-cap core mutual funds reveals that security selection serves as the principal driver of excess returns. Although sector allocation accounts for a considerable proportion of return variability over time, its contribution to active performance is comparatively limited. These findings underscore the importance of probabilistic reasoning and risk-aware decision making in the presence of uncertainty. Collectively, the evidence suggests that, within the realm of equity portfolio management, sustained outperformance is more closely associated with consistent security selection than with sector allocation decisions.
Aw et al. (Thu,) studied this question.