With the continuous improvement of software processes, it is possible to increase quality, to address different application domains and accelerate the development of software products. However, existing process modelling notations like the SPEM meta-model typically do not have appropriate constructs for expressing process variability. Thus, SPEM-based approaches such as SMartySPEM and vSPEM provide mechanisms for representing variabilities to address characteristics of different projects. Here, the authors empirically compared SMartySPEM and for variability representation in software processes models, aiming to analyze correction, time, and efficiency. The performed experiment provides preliminary evidence based on 11 participants and sample size N = 44. Participants took longer to comprehend diagrams in SMartySPEM. However, the correctness of SMartySPEM diagrams had a superior result and higher efficiency based on the median values and hypothesis tests. With regard to variability mechanisms, the diagrams modelled with SMartySPEM had a slightly lower efficiency and it took longer for modifying them, thus the correctness of the SMartySPEM diagrams had a superior result. Therefore, an initial body of knowledge indicated a positive efficiency of SMartySPEM for variability representation in process models, as well as potential improvements as the reduction in SMartySPEM diagrams complexity, which may contribute to its evolution.