Considering two samples of Portuguese SMEs: 582 young SMEs and 1654 old SMEs, using the two-step estimation method and quantile regressions, the empirical evidence allows us to conclude that the determinants of investment have a different impact on young and old SMEs, depending on a firm’ level of investment. In the framework of Acceleration Principle and Neoclassical Theories, the determinants are relevant in explaining the investment of young and old SMEs with high levels of investment. The Growth Domestic Product, as the investment determinant of Acceleration Principle Theory, has a greater impact on the investment of young SMEs with high levels of investment. Sales, as the investment determinant of Neoclassical Theory, have greater impact on the investment of old SMEs with high levels of investment. Cash flow, as the investment determinant of Free Cash Flow Theory, is important in explaining the investment of young and old SMEs with low levels of investment. However, cash flow has greater impact on the investment of young SMEs with low levels of investment. The empirical evidence obtained allows us to make suggestions for policy-makers and the owners/managers of Portuguese SMEs.

In this study, Aivazian, Ge and Qiu’s (2005) analysis using static panel models is extended to using dynamic panel estimators, considering data for listed Portuguese companies. The results confirm Aivazian et al.’s (2005) conclusion that an ordinary Least Squares (OLS) regression is not the best way to estimate the investment/determinant relationship. Investment decisions are probably dynamic, so the most suitable way to estimate the investment/determinant(s) relationship is using dynamic panel estimators. Alternatively a fixed effect panel model can be used, consistent with a first order autocorrelation. In this way, firstly, it is possible to determine more accurately the positive impact of sales (Neo-classic theory) and cash flow (Free Cash Flow theory) on the investments of listed Portuguese companies. Secondly, the positive effect of growth opportunities (Agency theory) is not overestimated when it seems to be the consequence of a first order autocorrelation. Using dynamic panel estimators permits correct measurement of dynamism in company investment decisions by examining the relationship between investment in the previous and the current periods.

This paper makes an important contribution to the literature on SMEs, namely investigating whether the relationships between determinants and investment are dependent on the level of investment. Based on a sample of Portuguese SMEs, using two-step estimation method, firstly using probit regression and secondly using quantile regressions, we find significant non-linearities in relationships formed between determinants and investment over the distribution of investment. In particular, we find that: 1) sales, age and growth opportunities are restrictive determinants of investment for low levels of investment, but positive determinants of investment for high levels of investment; 2) debt and the interest rate are restrictive determinants of investment but only for low and intermediate levels of investment; 3) cash flow is a positive determinant of investment, but is more important for investment regarding low levels of investment; 4) GNP is a positive determinant of investment, but only for high levels of investment; and 5) investment in the previous period is a positive determinant of investment in the present period, but only for intermediate and high levels of investment. The relevance of the various theories explaining firm investment depends on SMEs’ level of investment.

In this study we investigate whether the investment determinants of new SMEs differ from those of existing SMEs. To do so, we use two samples of Portuguese SMEs: 495 new SMEs and 1350 existing SMEs, and to estimate the results we use the two-step estimation method. The empirical evidence allows us to conclude that cash flow, age, growth opportunities and GNP are of greater importance for stimulating investment in new SMEs than they are in existing SMEs; sales are of greater importance in stimulating investment in existing SMEs than they are in new SMEs; and debt and interest rate are of greater importance in reducing investment in new SMEs than they are in existing SMEs. Also, the persistence of investment over time is greater in new SMEs than it is in existing SMEs. These findings suggest that problems of information asymmetry between SME owners/managers and creditors are particularly important in the context of new SME activity. As guidelines for economic policy, we suggest adding effective support through the creation of beneficial lines of credit designed specifically to support new S ME activity.