The reliability and the validity of the OLQ-13 in this population of non-institutionalized individuals aged 65 years and older was ambiguous, at least partly due to the poor performance of item b and item d. This problem has been reported before and seems to be resolved, at least partly, by excluding the items b and d from the analysis . The psychometric properties of the OLQ-11 (obtained by deleting the two items) were indeed better, in particular the exploratory factor solution. Where the underlying theoretical constructs could not be linked to the exploratory analyses of OLQ-13, this was to some extent possible in OLQ-11 with problems remaining due to items k and item m. The superior validity of OLQ-11 over OLQ-13 was supported by the better model fit in the confirmatory factor analysis. It is important, however, to acknowledge the relatively large unique factor variances in the model, suggesting substantial "noise".
The reported high correlation between item b and item c has also been found in other studies [10, 29, 30], and could be explained in the present study by interviewees perceiving these questions as similar.
The present study confirmed the multi-dimensional nature of SOC in the aging population, previously shown for other populations [8–10, 31]. Whether to view Sense of Coherence as a one factor model or a three factor model has often been debated in the literature [2, 8–10, 15, 32, 33]. This study therefore applied several criteria to extracting factors in the exploratory analyses, eventually suggesting a three factor model. Moreover, both the three factor and one factor solution were further tested in confirmatory analyses.
The present study focused on the reliability and the construct and face validity of the OLQ-13 among community-dwelling older individuals and suggested the OLQ-11. It did not look into the divergent validity by investigating whether SOC appears as a salutogenic construct distinct from quality of life and (absence of) depression. That this may be an issue was shown in a study on girls aged 14 to 18 years . Blom et al  concluded that symptoms of anxiety and depression were better captured in the OLQ-29 than in the specialized scales they considered. It would be interesting to investigate whether similar issues arise in clinical and non-clinical groups of older individuals.
The OLQ-13 has been translated and used in many countries and in different populations. Generally speaking, translation of scales and questionnaires requires explicit attention since translation may influence validity . No published information is available on the translation difficulties and resulting (lack of) equivalence of the OLQ-13 in Dutch.
Although a response rate of 67% is generally considered sufficient, this does not imply full representativeness of the population under study per se. In this study the percentages for the men and women match those of the general population (42% men and 57% women) for the participating municipalities . The over-sampling of the age group 75 and over prevented the bias of under representation of this group. However, this study aimed to assess the OLQ-13 scale and the items within it rather than to draw conclusions on the population under study. This makes issues of representativeness of less importance.
This study is unique in its mixed-method approach to the study of OLQ: it combines of qualitative and quantitative approaches/data. The added value of this combination lies in the quantitative part providing enough data to work with a separate construction and validation set, and the qualitative part of this study providing the detailed in-depth information necessary to understand what made particular items problematic for members of this population. The qualitative part gave the context that allowed for a better understanding of problems that presented themselves in individual items. Since the data for the qualitative part were collected before the quantitative analyses, they can be regarded as independent: neither the quantitative nor the qualitative data collection was influenced by previous results.
Interpretation of the Cronbach's alpha scores is problematic since these alpha scores are influenced by the number of items tested, which were higher for the scale as a whole and the comprehensibility dimension. This problem is illustrated by Olsson  in a study comparing the OLQ-29 and OLQ13, showing higher values for the OLQ-29. This study therefore also used split-half and inter-item correlations to assess reliability.