Harmonization of Neuroticism and Extraversion phenotypes across inventories and cohorts in the Genetics of Personality Consortium: an application of Item Response Theory.
van den Berg SM., de Moor MHM., McGue M., Pettersson E., Terracciano A., Verweij KJH., Amin N., Derringer J., Esko T., van Grootheest G., Hansell NK., Huffman J., Konte B., Lahti J., Luciano M., Matteson LK., Viktorin A., Wouda J., Agrawal A., Allik J., Bierut L., Broms U., Campbell H., Smith GD., Eriksson JG., Ferrucci L., Franke B., Fox J-P., de Geus EJC., Giegling I., Gow AJ., Grucza R., Hartmann AM., Heath AC., Heikkilä K., Iacono WG., Janzing J., Jokela M., Kiemeney L., Lehtimäki T., Madden PAF., Magnusson PKE., Northstone K., Nutile T., Ouwens KG., Palotie A., Pattie A., Pesonen A-K., Polasek O., Pulkkinen L., Pulkki-Råback L., Raitakari OT., Realo A., Rose RJ., Ruggiero D., Seppälä I., Slutske WS., Smyth DC., Sorice R., Starr JM., Sutin AR., Tanaka T., Verhagen J., Vermeulen S., Vuoksimaa E., Widen E., Willemsen G., Wright MJ., Zgaga L., Rujescu D., Metspalu A., Wilson JF., Ciullo M., Hayward C., Rudan I., Deary IJ., Räikkönen K., Arias Vasquez A., Costa PT., Keltikangas-Järvinen L., van Duijn CM., Penninx BWJH., Krueger RF., Evans DM., Kaprio J., Pedersen NL., Martin NG., Boomsma DI.
Mega- or meta-analytic studies (e.g. genome-wide association studies) are increasingly used in behavior genetics. An issue in such studies is that phenotypes are often measured by different instruments across study cohorts, requiring harmonization of measures so that more powerful fixed effect meta-analyses can be employed. Within the Genetics of Personality Consortium, we demonstrate for two clinically relevant personality traits, Neuroticism and Extraversion, how Item-Response Theory (IRT) can be applied to map item data from different inventories to the same underlying constructs. Personality item data were analyzed in >160,000 individuals from 23 cohorts across Europe, USA and Australia in which Neuroticism and Extraversion were assessed by nine different personality inventories. Results showed that harmonization was very successful for most personality inventories and moderately successful for some. Neuroticism and Extraversion inventories were largely measurement invariant across cohorts, in particular when comparing cohorts from countries where the same language is spoken. The IRT-based scores for Neuroticism and Extraversion were heritable (48 and 49 %, respectively, based on a meta-analysis of six twin cohorts, total N = 29,496 and 29,501 twin pairs, respectively) with a significant part of the heritability due to non-additive genetic factors. For Extraversion, these genetic factors qualitatively differ across sexes. We showed that our IRT method can lead to a large increase in sample size and therefore statistical power. The IRT approach may be applied to any mega- or meta-analytic study in which item-based behavioral measures need to be harmonized.