The International Personality Item Pool (IPIP) was born within a personality item-writing project organized by Wim K. B. Hofstee and his colleagues and students at the University of Groningen in the Netherlands (Hendriks, 1997; Hendriks, Hofstee, & de Raad, 2002). This project assumed "the lexical hypothesis," which is the notion that most important differences between people eventually become encoded in the natural language (Goldberg, 1981). But, whereas most lexical researchers have asked people to describe themselves and others with personality trait adjectives, the Gronigen collaborators believed that ratings on short, concrete behavioral phrases would be less subject to idiosyncratic interpretation than ratings on relatively abstract trait adjectives.
To generate personality-descriptive items, the Groningen group assembled three teams of five to ten members. Each team consisted of Hofstee, Hendriks, and de Raad, supplemented by two to seven advanced psychology students. The teams followed ten guidelines provided by Hofstee (Hendriks, Hofstee, & de Raad, 2002):
Three points of departure guided the item content. The first was the 90-facet AB5C model of personality (Hofstee, de Raad, & Goldberg, 1992), which organizes trait adjectives around pairs of the Big-Five personality factors. Team members individually wrote items, which were then discussed by the entire team as to whether items followed the ten guidelines and accurately represented a facet of the AB5C model. Teams as a whole decided whether items were kept, revised, or rejected. This process produced 909 items. Examples are Straalt vreuge uit (Radiates joy), Geeft mensen het gevoel dat ze welkom zijn (Makes people feel welcome), and Kan goed met mensen omgaan (Gets along well with others).
The second source of item content was the list of 1,557 personality-descriptive verbs compiled by de Raad, Mulder, Kloosterman, and Hofstee (1988). This list guided the production of 136 items such as Beledigt mensen (Insults people) and Vrolijkt anderen op (Cheers people up).
Finally, 266 items were written to cover the Intellect content in Factor V from American and German factor analyses of trait adjectives. This is because the Dutch Factor V is Rebelliousness or Spirit rather than Intellect.
The project became international when the 1,311 items generated by the Dutch teams were translated into American-English with the help of Lewis R. Goldberg of the Oregon Research Institute and German by Alois Angleitner and his team at Universität Bielefeld. Only items for which good English and German translations could be found were retained. The final, trilingual pool of 914 items was the beginning of the International Personality Item Pool.
Next, the focus of IPIP research shifted to the Oregon Research Institute in the United States. With support from an eight-year NIMH grant, Mapping Personality Trait Structure, Lewis R. Goldberg and Gerard Saucier solicited research participants from lists of homeowners in the Eugene-Springfield area. Roughly 500 men and 500 women between the ages of 18 and 85 initially expressed an interest in the project and completed a mini-inventory of 360 trait-descriptive adjectives in the summer of 1993. In the spring of 1994, around 850 of them then completed an inventory of 858 American English items from the trilingual item pool. Items were reworded to first person for the research, for example, Act wild and crazy, Pay attention to details, and Am full of ideas.
Thus was born the Eugene-Springﬁeld Community Sample (ESCS), a group of research participants who have now completed by mail over 30 surveys covering a wide range of topics, including personality traits, values and attitudes, vocational and avocational interests, possessions, current and past activities, aspects of psychopathology and of physical health, talents and skills, and exposure to potentially traumatic events both in childhood and adulthood. These surveys are described in an ORI Technical Report. Additional sets of IPIP items authored by Lewis R. Goldberg were included in the surveys. The current IPIP now stands at over 3,000 items. The administration of many widely-used commercial personality inventories to the ESCS allowed for the construction of IPIP scales to measure constructs similar to those in existing inventories. To date, over 400 such scales have been constructed.
The first public presentation of the IPIP project was a paper delivered by Goldberg (1999) at the 8th European Conference on Personality in 1996. Researchers embraced the international, integrative nature of the project, and various research teams began translating IPIP items into their own languages. Currently, the IPIP Translation Page lists the 40 different languages into which IPIP items have been translated. At the same time, authors of commercial personality inventories at the conference expressed concerns about possible copyright infringement. Concerns about job applicants using IPIP scoring keys to cheat on commercial inventories also arose. Discussions established that IPIP scales are not copies of those inventories, and the language used on the IPIP website clearly indicates that IPIP scales only measure constructs that are similar to those in commercial inventories and are not identical substitutes for them. An explicit warning about the foolishness of trying to use the IPIP to cheat during personnel selection was also posted on the website.
The discussion about the viability of the IPIP as an open-source project was continued at the 2005 meeting of the Association for Research in Personality (Goldberg, et al., 2006). Seven personality measurement experts in the discussion clarified the factors that have made the IPIP an increasingly popular resource, while noting what should be done to maximize the usefulness of the IPIP. Progress since the 2005 meeting has continued. In the words of Revelle, et al. (in press), "The initial development of the IPIP was controversial, as some believed that commercial developers could do a better job (Costa and McCrae, 1999). The citation count to the IPIP belies this belief. With at least 2141 Google Scholar citations to the original publication (Goldberg, 1999) and 1430 to the subsequent discussion (Goldberg et al., 2006) it is safe to say that open source personality measurement is a good idea."
The IPIP was originally conceived as resource for personality assessment professionals. The original IPIP Mission Statement read as follows:
"This IPIP Website is intended to provide rapid access to measures of individual differences, all in the public domain, to be developed conjointly among scientists worldwide. Later, the site may include raw data available for reanalysis; in addition, it should serve as a forum for the dissemination of psychometric ideas and research findings."
The publication of more than 600 IPIP-related papers indicates that the IPIP has been fulfilling its primary mission. What has become clear after nearly two decades in existence, however, is that the IPIP appealed to novices as well as professionals. The IPIP is particularly appealing to students undertaking personality research projects because they often have neither the funding nor the professional qualifications to purchase commercial personality inventories. Also, both students and professionals often wish to conduct their research on the Internet, and copyright restricts disallow the copying and reformatting of items from commercial inventories. The IPIP Consultant, John A. Johnson, reported at the 2005 ARP meeting (Goldberg, et al., 2006) that many novice users were confused about how to find and use IPIP materials. Emails seeking help have continued to increase in the ten years since that report.
As a consequence of the increasing diversity of needs of IPIP users, a major reorganization of the IPIP website was undertaken in 2015. The front page of the site was restructured into the following three sections: (1) a set of links for professionals and those acquainted with the IPIP to directly access items and scales; (2) a set of links for novices that explain how to find and use IPIP materials; and (3) a set of links pointing to background and miscellaneous information about the IPIP. In the reorganizational process, a number of existing Web pages were revised and new pages (including the present page) were created. Links to raw data sets were also provided, fulfilling the final point of the original mission statement. The site maintainers continue to welcome questions about the site and suggestions for future revisions.
Costa, P. T. and McCrae, R. R. (1999). Reply to Goldberg. In Mervielde, I., Deary, I., De Fruyt, F., and Ostendorf, F. (Eds.), Personality psychology in Europe, Volume 7 (pp. 29–31). Tilburg University Press, Tilburg, The Netherlands.
Goldberg, L. R. (1981). Language and individual differences: The search for universals in personality lexicons. In L. Wheeler (Ed.), Review of personality and social psychology: Vol. 2 (pp. 141-165). Beverly Hills, CA: Sage.
Goldberg, L. R. (1999a). A broad-bandwidth, public-domain, personality inventory measuring the lower-level facets of several five-factor models. In I. Mervielde, I. Deary, F. De Fruyt, & F. Ostendorf (Eds.), Personality Psychology in Europe, Vol. 7 (pp. 7-28). Tilburg, The Netherlands: Tilburg University Press.
Goldberg, L. R., Johnson, J. A., Eber, H. W., Hogan, R., Ashton, M. C., Cloninger, C. R., & Gough, H. C. (2006). The International Personality Item Pool and the future of public-domain personality measures. Journal of Research in Personality, 40, 84-96.
Hendriks, A. A. J. (1997). The construction of the five-factor personality inventory (FFPI). Academisch proefschrift, Rijksuniversiteit Groningen, The Netherlands.
Hendriks, A. A. J., Hofstee, W. K. B., & de Raad, B. (1999). The Five-Factor Personality Inventory (FFPI). Personality and Individual Differences, 27, 307-325.
Hendriks, A. A. J., Hofstee, W. K. B., & de Raad, B. (2002). The Five-Factor Personality Inventory: Assessing the Big Five by means of brief and concrete statements. In B. de Raad and M. Perugini (Eds.) Big five assessment. Seattle: Hogrefe & Huber.
Hofstee, W. K. B., de Raad, B., & Goldberg, L. R. (1992). Integration of the Big-Five and circumplex approaches to trait structure. Journal of Personality and Social Psychology, 63, 146-163.
Revelle, W., Condon, D. M., Wilt, J., French, J. A., Brown, A., & Elleman, L. G. (in press). Web and phone based data collection using planned missing designs. In G. Blank, R. Lee, & N. Fielding (Eds.), Handbook of online research methods. Thousand Oaks, CA: Sage Publications.