Apart from recognizing that SIDs in CHR patients may underlie a more complex pattern, with critical methodological details necessarily lost in a broader review of the literature (Schecklmann et al., 2013), it should also be noted that all reported group differences for smell identification were small in absolute terms (i.e., about 1–3 test items), and our own data indicated less variance for odor identification compared with all other olfactory function measures (cf. Fig. 8). Moreover, the use of different olfaction tests (Sniffin’ Sticks, UPSIT/BSIT) may impede cross-study comparisons. Although both standardized tests have been found to be reliable instruments for evaluating smell identification deficits in Parkinson’s disease, overall test scores had only 58% common variance (Silveira-Moriyama et al., 2008). The specific Sniffin’ Sticks and UPSIT test versions used in the present and the prior studies differ in a variety of methodological aspects, including the delivery procedure (felt tip pens vs. scratch and sniff booklets) and the number of odorants (16 vs. 40 vs. 12), which may be of critical importance for revealing and understanding smell identification deficits in schizophrenia and individuals at clinical high risk for psychosis.
