Definition:  Measurement procedures that present respondents with ambiguous material for the purpose of producing information about unconscious processes and structures.

         Description.  Published in 1921, the most well-known projective device, the Rorschach, was developed to assist in differentiating between normal and clinical groups.  The Rorschach consists of 10 cards with symmetrical inkblots.  The examiner hands the card to the subject and asks “What might this be?”  The examiner continues through all 10 cards and records the free association the respondent makes with each card.  After this initial sequence the examiner again goes through each card, asking the respondent to indicate the material on the card that stimulated the particular responses.

While the Rorschach is the predominant projective technique, mainstream testers commonly hold it in disrepute.  Even Rorschach advocates sometimes attempt to deflect criticism by referring to the Rorschach as a technique and not a test (cf. Aronow et al., 2010).  The Rorschach has enjoyed a resurgence, however, as a result of efforts by Exner (1978, 1986) and colleagues to establish more standardized procedures for administering and scoring the instrument.  Exner (1986) provided an excellent summation of the key projective assumption of the test:

It is important to remember that Rorschach answers are, in microcosm, a unique and valuable behavioral sample reflecting the way the individual is most likely to respond in a problem solving situation where there are few rules or principles directing the ‘psychological traffic.’ In the Rorschach, the individual is ‘on his own,’ forced to use the behaviors with which he [sic] is most comfortable, which are easiest for him to display, and which, in his judgment, will lead to acceptable performance.  One of the most important features of the Rorschach is that it is ‘nondirected’ and does force the individual to display his ‘psychological wares’ in coping with the situation.  When the Comprehensive System was developed, one point became clear above all others:  the importance of keeping the task as free as possible from externally induced direction. (p. 59)

Parker, Hanson, and Hunsley (1988; also see this review) conducted a meta-analysis to compare the published psychometric properties of the MMPI with the Rorschach.  They collected data about test reliability (including internal consistency and rater agreement estimates), stability (test-retest), and convergent validity (correlations with relevant criteria).  Interestingly, Parker et al. found an insufficient number of discriminant validity reports to be able to report a comparison of the two instruments in this category.  Parker et al. (1988) combined test subscales to produce the following psychometric estimates:  (a) for reliability, an overall r of .84 for the MMPI and .86 for the Rorschach; (b) for stability, an overall r of .74 for the MMPI and .85 for the Rorschach; and (c) for convergent validity, an overall r of .46 for the MMPI and .41 for the Rorschach.  Parker et al. concluded that despite the MMPI’s reputation as the superior instrument, both the MMPI and Rorschach appear to possess comparable psychometric values.

For another perspective, read this Wikipedia page or watch this video.