Many of the questionnaires and rating scales used in psychiatry for research and clinical practice purport to measure the same constructs. For instance, there are at least 280 instruments to identify the construct of depression, alone. First, this limits comparability and linkage between studies, replication and meta-analyses because each instrument has its own scoring. Second, limited overlap in symptoms (items) across different instruments for the same construct leads to ambiguity and vagueness in the definition and validity of mental health conditions, so that researchers frequently develop yet more instruments ‘better’ to measure their own constructs. Less decisive colleagues may choose two instruments for the same construct: multiple analyses and selective reporting deepen the reproducibility crisis. Finally, it makes the choice of measurement instrument complex and a reasonable desire to support comparability creates pressure to use a well-known instrument, regardless of its construct validity.