[4][5][6] CORE-OM has 34 items all answered on the same five level frequency scale asking about the respondent's state over the last week.
It was originally designed and developed in response to a research funding call from the UK Mental Health Foundation which required that the content must cover domains of well-being, problems, functioning and risk.
The copyleft status was intended to remove cost barriers to using the instruments while ensuring that they weren't mutated into many non-comparable forms.
When CORE was launched in 1998 it rapidly became clear that there were several similar initiatives including theOutcome Measures work, in which the Outcome Measure-45 Outcome Questionnaire 45 led by Professor Michael Lambert in the USA and, also from the US, the ORS/SRS system led by Scott D. Miller and his colleagues all of which share the idea of a central "core" or issues being evaluated.
The Therapy Meets Numbers resource now offers COREbots as an online completion system.