The aim of this study was to assess the factorial structure of the scale, the method's effect associated with its negative items, its temporal invariance, and factorial invariance according to sex. For this purpose, three samples were collected, an initial sample of 200 participants, a second sample of 461 participants and a third sample of 107 participants; making a total of 768 Peruvian university students. Other instruments were applied together with the EROS scale in order to measure satisfaction with life, anxiety, stress and depression. Regarding the results, in the initial sample it was found that the original scale containing positive and negative items does adequately fit the data (RMSEA = .19; CFI = .77; TLI = .71) and also evidence was found supporting the existence of a methodological effect associated with the negative items. It was also found that version B of the scale which only has positive items data fits the data (RMSEA = .13; CFI = .96; TLI = .95). In the second sample it was found that version B still had a good fit to the data in a larger sample (RMSEA = .07; CFI = .98; TLI = .98). In addition, it was found that the scale can be considered invariant according to sex and presents validity based on other constructs. In the third sample it was found that the test-retest reliability of the scale was adequate (.70 [CI95% .593–.788]) and also evidence was found in favor of the temporal invariance of the scale. It is concluded that the scale formed only by positive items presents more robust psychometric properties and constitutes a better alternative to measure the level of reward provided by the environment.

Background Positive relationships are one of the most important components within the PERMA model since they facilitate the development of the other components. However, in the scientific literature, few instruments have been identified with solid psychometric properties that measure positive relationships in university students and adequately represent the construct. Therefore, the study aims to develop and study the psychometric properties of the PRI + 19 positive relationships scale through Confirmatory Factor Analysis, factorial invariance, and relationship-based validity with other variables. Method A pilot sample of 201 university students (43.8% men and 56.2 women) between the ages of 18 and 34 (M = 20.9; SD = 2.74) was collected. The confirmatory sample consisted of 450 university students of both sexes (30.2% men and 69.8 women) between the ages of 18 and 35 years (M = 21.9; SD = 3.15). Along with the PRI + scale, other instruments were applied to measure satisfaction with life and psychological well-being. Results In the pilot study, the Exploratory Factor Analysis showed the presence of three factors that could explain 54.5% of the items. In the confirmatory study, the Confirmatory Factor Analysis showed that the model of three dimensions related to 19 items presents the best adjustment indexes compared to other models (χ2 = 541.61; df = 149; CFI = 0.97; TLI = 0.97; RMSEA = 0.077 [IC90% 0.070 ‒ 0.084]). The scale also showed evidence of being strictly invariant for the groups of men and women. Finally, it was shown that the development of the positive bonds dimension positively predicts psychological well-being (0.35) and life satisfaction (0.20). The positive relationship management dimension positively predicts psychological well-being (0.28) and life satisfaction (0.29). Similarly, the integration dimension positively predicts psychological well-being (0.48) and life satisfaction (0.52). Conclusion This study suggests that the PRIM + 19 scale is a useful tool from which valid and reliable interpretations of positive relationships in Peruvian university students can be obtained.