It is suggested in this article that a firm's mandatory disclosure policy can be summarized in a single factor characterizing the type of firm. For voluntary disclosure policy a firm-size variable should be included in the model, in addition to the firm-type factor. The fit of the capital structure and growth factors is tested for the basic saturated model. In the next phase, the possibility of combining these two factors into a single factor, resulting in a more parsimonious model, is tested. The test in favour of the one-factor model is clearly passed. The results add to our current understanding of the determinants of interim reports in a relatively new interim reporting practice, namely in Finland. Compared to conventional regression models with many independent variables, this study reports a model that reduces the number of parameters. Furthermore, valuable insight is gained into the differences between the determinants of mandatory and voluntary disclosures. This, in turn, should be able to help legislators and regulators in their work.