This research is a systematic, in depth empirical test of the strong form of the efficient market hypothesis (EMH) using the dual-fund industry as the research subject. Unlike most strong-form EMH research, this study deals with a small, homogeneous sector of the investment company industry with a comparable origin date. To obtain homogeneity of the research subjects, the sample size is necessarily small (7), thus, making it difficult to find statistically significant results. In general, portfolio performance is negatively correlated with variability in measures of portfolio characteristics such as the major mix, common stock categories, portfolio turnover, etc. The better-performing dual funds were more consistently managed while the lower-performing companies had significant and sometimes frequent changes in portfolio policies. In line with the efficient market hypothesis, "passive" management, i.e., low turnover, few changes in major mix or common stock composition, shows better results in the dual-fund industry from inception through 1973.