Mild cognitive impairment (MCI) is a condition where a person has some problems with cognition that are unexpected for their age, but that don’t strongly impact daily life. One of the common ways to identify it is to use Petersen's criteria.
Petersen’s criteria were initially created to aid in the identification of individuals in a transitional period between normal aging or cognitive function and early AD or dementia such that, if therapeutic interventions are available, clinicians may be able to intervene. The transitional period is generally referred to as MCI and is defined by five criteria:
Subjective memory complaint (at least six months)
An objective memory impairment (at least 1.5 SD below education and age-matched controls on a Mini-Mental State Examination (MMSE) subtask)
Normal general cognitive function impairment (test performance of at least 1.5 SD below education and age-specific norms)
Preserved essential activities of daily living (score of less than 26 on Activities of Daily Living Scale)
Absence of dementia (Diagnostic and Statistical Manual of Mental Disorders-IV)
While there is some controversy over standardization of its diagnosis, memory complaints and assessment of general cognitive function are the most consistently measured criteria. Moreover, discrepancies across studies for MCI diagnosis might be explained by differences in operationalization of the criteria, differences in setting, participant criteria, and length of follow-up. The main controversial issues revolve around algorithmic compared to clinical classification, reliability of clinical judgement, changes in cognitive performance over time, and predictability or incorporation of biomarkers within the criteria.