favoring of profitability, and the second one, although significant in both analyses,
shows a negative correlation with profitability while using this regression analysis a
positive relationship in the four equations of the study is visible. The reason for this
reversal of the relation lies probably on the control of specific unobservable
characteristics of firms, as obtained by the method of fixed effects.
3.2 Robustness and endogeneity
Aiming at evaluating the robustness of the results, the equations were recalculated
using a proxy of the independent variables, defined in a way similar to other studies in
international markets (Deloof, 2003; García-Teruel and Martínez-Solano, 2007) and
return on invested capital (ROIC), as proxy for profitability. The results are, again,
similar to those obtained using the variables determined for the Portuguese situation,
making them robust (for concision, these results are not presented, being available
upon request).
To control the possible effect of this endogeneity problem, the regression of the
equations was made also resorting to instrumental variables. The first lags of the INV,
AP, AR and CCC variables were used as an instrument. Table VI presents the results.
The results are similar to those found in Table V, except for the AR variable, which
displays a positive relationship. In this sense, this result does not confirm the negative
effect that a decision to provide customers with extended terms of payment may have on
corporate profitability and can be explained because the costumers require, from firms
with declining profitability, more time to assess the quality of products (Deloof, 2003).