We are sometimes asked how to interpret individual IPIP scale scores, for example, "How high does a person have to score on the Extraversion scale to be considered an Extravert?" We are also sometimes asked if we have manuals or interpretive guides that explain what is likely to be true for people who score within certain ranges on IPIP scales. If someone does score within the extraverted range, what else can be said about that person? This page provides some answers to these questions.
First, the IPIP website does not contain manuals or interpretive guides for explaining how to interpret specific scales. For most of the constructs listed on the IPIP website there is an extensive body of research that was published prior to the development of the IPIP representations of these constructs. At the bottom of both the Multi-Construct IPIP Inventory page and the Single Construct IPIP Scales page is a list of publications that refers to this research. There is also a growing body of publications describing studies that have used IPIP scales; a non-exhaustive list of these appears on the IPIP-Related Publication page. IPIP scale users who want to know what people on the low and high ends of a particular construct are like should acquaint themselves with the relevant research literature.
To interpret individuals' scores, one might calculate the mean and standard deviation (SD) for a sample of persons, usually of the same sex and a particular age range, and interpret scores within one-half SD of the mean as "average." Scores outside that range can be interpreted as "low" or "high." If the scores are normally distributed, this would result in approximately 38% of persons being classified as average, about 31% as low, and 31% as high. We recommend computing means and standard deviations in one’s own sample for reasons explained on the Norms page of the IPIP website.
An alternative method for showing respondents where they stand with respect to a group of respondents is to divide a set of scores into five equal parts, which are called quintiles. Labels for the scale anchors describe the lowest 20% and highest 20%, the label "average" is used for the middle 20%, and the remaining quintiles are labeled "somewhat." For example, labels for the quintiles on a scale that ranges from introversion to extraversion would be introverted, somewhat introverted, average, somewhat extraverted, and extraverted.
One of the above schemes usually works well enough for providing feedback to participants. When one conducts statistical analyses, however, one should try not to pigeon-hole individuals into type categories like introvert and extravert, given that introversion-extraversion is a continuum. Most research studies can use continuous statistical analyses of the full range of scores, such as some form of regression analysis. And even when one provides feedback to participants, one can show them where their scores lie on the full continuum of scores rather than telling them what type of person they are. In short, we caution against interpreting IPIP scale scores in terms of categories or sorting respondents into groups based on their scores.