Introduction

Validity is one of the most fundamental prerequisites for the scientific value of any research process. It refers to the extent to which a measuring tool accurately captures the concept for which it was designed. In practice, this means that a scale or research instrument is considered valid only when it can precisely reflect the phenomenon or characteristic it aims to measure. For example, a questionnaire that claims to assess an individual’s worry cannot simultaneously record indirectly other concepts, such as generalized anxiety or stress, without clear distinction. Validity is closely related to the concept of reliability, yet it essentially differs. A measuring tool may be reliable, meaning it consistently produces stable results, but not valid if those results do not correspond to the theoretical construct it intends to measure. For this reason, in scientific research it is essential to check both parameters simultaneously.

Calculation and Assessment of Validity

The assessment of validity is carried out through repeated applications in populations that are representative of the research purpose. An instrument is considered valid when, in different applications, it continues to accurately reflect the concept it aims to measure. In this way, it is proven that the instrument is not influenced by external or random factors but remains focused on its research objective. The process of calculating validity involves seeking evidence that the measuring tool is both theoretically and practically related to the concept under study. This may be achieved either through comparison with other established tools or through statistical methods, such as factor analysis, which indicate whether the individual components of the tool reflect the theoretical construct it seeks to measure.

Types of Validity

Validity is not a single concept but encompasses different forms, each of which examines a different dimension of measurement. Content validity refers to whether the questions or variables of a tool sufficiently cover the theoretical field of the concept. For example, a tool designed to measure depression must include questions on mood, sleep, and energy, and not solely on one dimension. Face validity relates to whether a tool appears, at first glance, valid to participants and experts; although it is not a strong form of evidence, it functions in a supportive role. Criterion validity is divided into two types: concurrent validity, when the results of the tool are correlated with those of already established tools, and predictive validity, when the results can forecast future behaviors or phenomena. Finally, construct validity examines whether the tool measures the abstract theoretical construct it claims to measure. Construct validity is confirmed through factor analysis, through the method of known groups that compares populations theoretically expected to differ, through convergent validity when the tool is positively related to other similar tools, and through divergent or discriminant validity when it clearly differentiates itself from tools that measure different concepts.

Importance for the Research Process

Validity, combined with reliability, constitutes the foundation upon which scientific documentation is built. When a measuring tool demonstrates high validity, the data collected are considered strong and can be utilized for conclusions with both research and practical value. Conversely, a lack of validity renders the results questionable and significantly limits their usefulness. In published studies, it is necessary to explicitly report the indicators of reliability and validity of the instruments used. Only in this way is scientific transparency ensured and the possibility created for studies to be evaluated, replicated, and compared with others.

Conclusion

The concept of validity is crucial to the quality of scientific research. It is not sufficient for a tool to provide stable results; it must also measure precisely what it claims to measure. The different forms of validity—content, face, criterion, and construct—serve as the means through which the credibility of a tool is documented at both the theoretical and practical level. Without clear reference to validity and reliability, the findings of a study are limited and can only be accepted with reservations. On the contrary, when researchers invest in proper methodology and provide evidence of validity, the results gain increased weight, contribute to the advancement of science, and are meaningfully applied in practice.