Control variables that stand out significantly in the
regression models are firm size, age, debt in capital
structure, diversification, and R&D strategy. Firm
size (SIZE) is positively associated with profitability,
suggesting the existence of economies of scale. That
is, the larger the size of a firm, the more profitable it
is. Firm age (AGE) is negatively associated with all
performance indexes, indicating that the older the
firm, the less competitive and profitable it is.