This article explores the extent to which established sector classifications continue to provide meaningful insights into the financial underpinnings of firms. Utilizing a contemporary cross-sectional sample of 500 unique S&P 500 firms, the study constructs a parsimonious set of financial-statement-based ratios capturing profitability, leverage, liquidity, interest coverage, efficiency, and cash-generation capacity. These indicators are analyzed through a combination of non-parametric inference, supervised machine learning, and unsupervised clustering. The findings indicate that sector membership accounts for only a portion of the cross-sectional variation in firms' financial ratios. Supervised-learning models have been shown to achieve a maximum validation accuracy of 49.3%, with the broader set of imbalance-sensitive metrics reported across models likewise confirming only partial recoverability of sector labels from accounting data. Concurrently, the unsupervised clustering process yielded nine economically interpretable groups that transcend conventional sector boundaries, thereby reflecting distinct combinations of profitability, leverage, liquidity, and cash-generation patterns. The findings of this study indicate that these accounting-based clusters exhibit lower within-group dispersion than sector labels in most of the ratios examined. An exploratory temporal comparison suggests only moderate persistence of group membership across subsequent annual reporting periods. The findings indicate that conventional sector designations persist in their usefulness, yet they prove inadequate in fully encapsulating the accounting structures of firms. Consequently, accounting-based clustering offers an economically interpretable complementary perspective on firm similarity, especially when the objective is to compare firms based on financial structure rather than nominal industry membership alone. As the analysis is primarily cross-sectional, future research may further examine the temporal stability of these accounting-based peer groups and test their portability across alternative firm universes and market settings.
Forradellas et al. (Fri,) studied this question.