The PHI is based on the conceptual integration of current approaches to defining and measuring well-being. Our results suggest that the PHI is a consistent and valid instrument to provide an index of well-being.
The PHI has some noteworthy advantages relative to previous composite indices of well-being. From a conceptual point of view, this is the first instrument that attempts to cover the main domains of well-being described in current theories and research in the area. The PHI was designed taking into account prevailing controversies on the eudaimonic versus hedonic distinction and the remembered versus experienced approach. All these aspects of well-being are relevant, and integrative measures should be aware of the complexity of the well-being construct [18, 31].
Compared with other recently published brief well-being instruments, the PHI indeed encompasses a more thorough sense of the construct. For example, the MHC-SF  measures hedonic, eudaimonic, and social well-being but does not include experienced well-being. Also, the WEMWBS , in both its 7-item and 14-item versions, comprises positively phrased statements covering both hedonic and eudaimonic aspects of well-being, including positive affect, satisfying interpersonal relationships, and positive functioning. However, it does not include a specific item covering life satisfaction and does not cover experienced well-being or social well-being. Another recent brief index of well-being is the FS , which “was designed to measure social-psychological prosperity [and] to complement existing measures of subjective well-being” (p. 144). The FS is an eight-item scale that aims to provide a single index covering aspects of social capital, flow, social relationships, and a general sense of psychological prosperity (i.e., only partially covers some eudaimonic aspects of well-being). The authors who developed the FS used several well-known, validated instruments like the ones used in our study (i.e., the SHS, SWLS, PANAS, and SPWB) to assess the FS’ convergence validity. Yet, the scale was initially validated using only samples of university students.
Unlike other scales, the PHI includes a experience well-being section. Our data support that remembered and experienced well-being are related but different constructs. It is important to note that the experienced well-being section can be included or not in the index depending on the needs of the researcher and the characteristics of the sample. For example, in very small samples as well as for individual assessments, data from specific experiences that happened the day before, which is measured in the experienced well-being section, could be biased due to non-representative events (e.g., a sudden stressful event) that occurred the day before. On the contrary, larger samples make these random effects irrelevant as positive and negative non-representative events tend to equally happen compensating this potential source of bias. In sum, our index includes two separate scales assessing remembered and experienced well-being. Although these two subscales can be used separately, we suggest using them jointly especially when assessing the well-being of a community or a large sample.
Moreover, beyond these conceptual aspects, the PHI has distinctive methodological features. All the items included in the scale were empirically selected after being contrasted with widely used measures of each well-being domain. The study sample was also larger and more culturally diverse than in previous initial validation studies of similar brief scales.
Most notably, no other brief scale allows the use of each of its items as indices of different well-being domains. In designing and validating the PHI, we aimed for it to provide both a composite measure and individual measures of the different facets of well-being. As such, the PHI can be a valuable diagnostic tool when its items are used as individual and independent indicators. Although using a single-item scale implies diminished psychometric properties, it has been noted that this allows for an efficient assessment when needed . Moreover, our data showed that the capacity to detect differences among countries was equal or even slightly better when measured by our single-item subscales compared with other larger scales. This strength could be due, at least in part, to the use of an 11-point Likert scale. Although there is no consensus on the effect of an increase in the number of categories of a scale, it may foster variability. While some authors defend the idea of using no more than 7 categories , others favor the idea of using more categories . In their meta-analysis, Saris and Gallhofer  conclude that using an 11-point scale does not harm the reliability and validity of an instrument. According to this meta-analysis, it is more relevant to use a scale with a middle point and with clear, short labels for the two extremes. Both requirements are fulfilled in our scale. Moreover, an empirical study examining the role of different response options in the context of assessing subjective quality of life concluded that using a 10-point scale yielded better outcomes .
Finally, contrary to previous scales, we developed and validated the PHI for seven languages and nine countries, which increases its cross-cultural value. Although some versions may be refined in the future, this initial validation tentatively allows the use of the PHI in different countries and cultures. And, more relevant for cross-cultural research, the items included in the scale were chosen so that they maximize the convergent validity for the whole set of countries.
Our data support the fact that the PHI presents good psychometric properties. Given the nature of the measure, it is not surprising that the PHI positively correlates with validated measures of life satisfaction, positive affect, and eudaimonic well-being, and negatively correlates with negative affect. This correlation pattern suggests that the PHI reliably measures different aspects of well-being. The internal consistency of the PHI was very good for all language versions and inter-item correlations were consistently high. Some authors have warned against high homogeneity as it may indicate that several items have been paraphrased ; however, this is not our case. Instead, each of the items assesses a totally different dimension of well-being. Thus, the high homogeneity within the PHI may suggest the existence of a single construct. In fact, our principal components analysis indicates that the PHI has a single structure even as it integrates a complex conception of well-being involving its different aspects. Future research should confirm the factor structure in another sample (i.e., confirmatory factor analysis) and then verify the presence of measurement invariance across different language versions of the index .
We also acknowledge some limitations of this initial study. First, it would have been ideal to start with a larger pool of initial items. Due to the difficulties and costs of working with seven versions of the scale, we tried to select the best items before starting the translation and validation processes. Second, our study was conducted online. Although research has found that web-based surveys provide results as valid as those gathered with more traditional methods , we cannot completely rule out the existence of biases affecting web-based surveys that may not have yet been discovered. Nevertheless, our pattern of results is robust (in terms of internal consistency and validation indices of the PHI), which counters this possibility. Third, it is possible that some shared common variance is due to the assessment method. Finally, despite the effort to include a wide range of countries and languages, we were not able to incorporate other important languages (e.g., French and Chinese) and geographical areas (e.g., Africa) into the study. Furthermore, although the sample composition was larger and more heterogeneous than the samples used to validate similar instruments, the data in this study should not be considered representative of each country. Even so, the cross-national consistency of the results and the good psychometric properties of the PHI in all languages and participating nations are still noteworthy.
We are aware that the use of a self-report retrospective approach, such as the one used in the PHI and the Gallup study , does not completely preclude memory and judgmental biases when assessing experienced well-being. A better measurement option would involve costly procedures, as in the original DRM , or a sophisticated experience sampling method [6, 67]. Yet, an alternative and simpler measure of experienced well-being, such as the one used in our study, has shown to provide information different from typical remembered well-being measures .