An OPI is a test of a candidate's English language listening comprehension and speaking ability, conducted under controlled conditions by two certified OPI raters. It can be administered face-to-face or via telephone. The OPI cycle consists of a warm-up, to include autobiographical information; level checks, to assess ability to perform linguistic tasks at a base level; level probes, to determine ability to perform linguistic tasks at the next higher base level; and a wind down.
Candidates are rated on an 11-point scale, ranging from "0," no functional proficiency, to "5," educated native-speaker proficiency, with plus levels (0+, 1+, 2+, 3+, 4+) assigned to candidates who demonstrate inconsistent proficiency at the next higher base level. An OPI rating of "1" exemplifies "survival proficiency," while a "2" represents "limited working proficiency" and a "3" "general professional proficiency."The appraisal factors considered at each level (though not equally weighted) are vocabulary, grammar, pronunciation, fluency, linguistic tasks, and socio-linguistic/cultural awareness.
The OPI has the unique advantage of being a standardized method of measuring actual proficiency in language skills required to function in given life/job situations, as well as a testing tool with low risk of compromise. However, it is costly in terms of training and staffing requirements and its reliability is dependent on a human element, i.e. the competence/performance of OPI raters.