I do psychology and when i tested a number of young people using the moca cognitive assessment they failed? do they have dementia?

Be very careful: about diagnosing or using labels w/out proper training and experience. Start w/reading the manual for the MOCA, an instrument I'm not familiar with. Then consult w/an expert who uses the test. Study up on neuroscience. There are many aspects to cognition, many types of cognitive processes. Keep growing and you will be very helpful to the needs of our world. The very best to you.

Neuropsychologist : Dementia is a very serious diagnosis and should NOT be based on the findings of one single test. The MOCA has only been validated for mild cognitive impairment, not full dementia. The patient needs a full evaluation administered by a neuropsychologist who specializes in geriatric issues. A comprehensive battery of tests will be administered to indicate a much more comprehensive clinical picture.