Research purpose: The main purpose of this study was to examine the discriminant and convergent validity of two personality measures that measure the big five personality factors: the longer Basic Traits Inventory (BTI) and the shorter Ten-Item Personality Inventory (TIPI).

Motivation for the study: Researchers have indicated a need for shorter personality measures, such as the TIPI, to assess personality dimensions. This study assessed the validity of the shorter measure in comparison with the BTI, which is considered cross-culturally valid in the South African context.

Research approach, design and method: This study used a quantitative research design. Both personality measures were administered manually to a convenience sample of student participants (n = 662), and data were analysed through factor analysis utilising oblique rotation for all items.

Main findings: The main findings indicate that, although the construct validity of both measures was satisfactory, the TIPI yielded unsatisfactory reliability.

Practical/managerial implications: The BTI is a more reliable measure than the TIPI, which should only be used when time is limited.

Contribution/value-add: In addition to providing insight into how the length of an assessment impacts on the reliability of a measure, this study further reinforces the use of the basic traits inventory as a measure that reliably measures personality in South Africa.

In South Africa, the use of psychological assessment is governed by the Employment Equity Act (Act No. 55 of 1998), which states that:

psychological testing and other similar assessments are prohibited unless the test or assessment being used (a) has been scientifically shown to be valid and reliable, (b) can be applied fairly to all employees, and (c) is not biased against any employee or group. (Republic of South Africa, 1998, p. 9)

The onus is therefore on the psychologist to acquire and utilise knowledge that will allow them to develop shorter personality measures from which more rapid decisions can be made in comparison with longer personality questionnaires (Van Eeden, Cilliers & Van Deventer, 2008). However, irrespective of its length, a personality measure requires a demonstration of satisfactory psychometric properties in line with South African legislation (Meiring et al., 2005). According to Friedenberg (1995), an effective test displays three important psychometric properties: firstly, the test is valid, secondly, the test is reliable and, thirdly, it contains items that have valid item statistics.

It is widely accepted that long questionnaires have better psychometric properties than short questionnaires (Gosling et al., 2003). Most test administrators today would be very concerned if a test consisted of only a few items. A study by Burisch (1997) shows that the psychometric advantages of a long test is not always what one would expect. He compared subsets of two relatively short depression scales (nine and eight items respectively) with much longer ones (50 and 28 items respectively). The selected scale subsets were based on their content, and in 10 out of the 19 cases the selected subsets performed psychometrically better than the longer measures; in other words, curtailing scales enhanced rather than attenuated their validity. Burisch (1997) suggests that when a test is being developed, it is not necessarily the number of items included that is important, but rather the quality of the item definitions in measuring a specific construct.

However, there are also several limitations of using shorter personality measures. In the study by Gosling et al. (2003) three limitations were identified. Firstly, there was a decrease in the reliability properties compared to longer questionnaires with standard multi-item measures. Secondly, the short questionnaire was less reliable, converged less strongly with the big five personality measure and had weaker correlations with other variables. Thirdly, the individual facets of multi-faceted constructs are not always measured accurately, and therefore a longer personality questionnaire is preferable.

The FFM summarises personality into five broad theoretically and operationally defined dimensions, namely Neuroticism, Extroversion, Openness to Experience, Agreeableness and Conscientiousness. Neuroticism indicates how calm and self-confident an individual is, as opposed to being insecure and anxious. Extroversion measures how confident, social and assertive a person is, or, conversely, how introverted (withdrawn, quiet and reserved). Openness to Experience measures the extent to which an individual is imaginative and curious, as opposed to being closed minded and narrow thinking. Agreeableness indicates whether an individual is more warm and cooperative than unpleasant and disagreeable. Finally, Conscientiousness is the degree to which a person is organised and responsible, as opposed to being impulsive and irresponsible (Hofmans, Kuppens & Allik, 2008; Pervin & John, 1999).

Since its development, the FFM has been extensively revised over the past five decades (Rothman & Coetzer, 2002). These revisions, plus an accumulation of information in support of the model, means that the construct validation of these traits is now more securely established than before. This is undoubtedly why the five-factor trait model has captured so much interest and been the foundation for the development of personality questionnaires such as the Basic Traits Inventory (BTI) and the Ten-Item Personality Inventory (TIPI).

There are many characteristics that distinguish this questionnaire as a long personality questionnaire, with the most obvious being that it takes at least 45 minutes to complete. Many items were included in the questionnaire to specifically ensure that the questionnaire could be applied cross-culturally and to reduce bias against any race, gender or language groups in South Africa. Unlike some other personality questionnaires, the items are written in a positive manner and words like ‘never’, ‘not’, or ‘no’ were not used in the construction of the items (Taylor, 2004). According to Taylor (2004), items that are worded negatively or are negatively keyed can cause conceptual confusion. Therefore, wording the items in a positive manner produces less confusion and enables respondents to quickly recognise and understand the word or a statement. To ensure the cross-cultural suitability of the BTI, all items were screened for appropriateness with regard to content and comprehensibility. They are presented in blocks, there are no reverse scored items and the response categories of the five-point Likert scale are clearly labelled.

Another characteristic of this long personality questionnaire is that it includes factors and facets that provide a broader view of the five personality factors. The BTI consists of five factors and underlying facets. The factors included in this inventory are: Openness to Experience, Conscientiousness, Extroversion, Agreeableness and Neuroticism. The five factors are subdivided into five facets, except for Neuroticism, which has four facets. In addition, the BTI includes a measure of social desirability. Some of the facet scales in the NEO PI-R were included in this questionnaire, as the NEO PI-R is also structured around factors and facets. In addition, due to an extensive literature review by Taylor (2004), some new scales were included in the BTI not included in the NEO PI-R.

According to Taylor and De Bruin (2006), the BTI is an easy-to-use and easy-to-understand personality inventory. No psychological terminology is used in the questionnaire and the language is what most people would use in everyday life. The items are as short as possible so as to be clearly understandable. The BTI can be used for recruitment and selection purposes, staff development, educational settings, psychodiagnostics, counselling and research.

To expand on their study of the TIPI, Gosling et al. (2003) examined the convergent and discriminate correlations between the TIPI and the NEO PI-R scale and facet scores. This exercise presented strong convergent correlations between these two questionnaires, ranging from .56 for Openness to .68 for Conscientiousness. In addition, the correlations of the BFI and NEO PI-R were compared. These correlations were then compared with those of the TIPI–BFI and the TIPI–NEO PI-R. It was concluded that although, as expected, the correlations between the BFI and NEO PI-R were stronger, the correlations between the TIPI and the other two established five-factor measures were very similar, with only a few differences. Overall, the findings provided proof of the construct validity of the TIPI.

In the wake of these studies on the TIPI, more research has been done on this questionnaire in the last few years. Muck et al. (2007) developed a German version of the TIPI (TIPI-G). The factor structure, convergent and discriminant validity, and the correlations of a German version of the adapted NEO PI-R were investigated. The results showed that the five factors of the TIPI-G can provide a satisfactory representation of the big five factors of longer versions of the five-factor trait model. However, as these questionnaires did not measure all the facets of the big five, the use of the TIPI-G was recommended only when time was limited.

The central benefit of the TIPI is that it extends the scope of studies in which the big five personality factors can be measured. Another advantage of the TIPI, as described by Gosling et al. (2003), is that it is a standard questionnaire that can be used by all researchers. Through the use of a standard questionnaire, psychometric properties and external correlates are improved, which will assist other researchers in further studies. Secondly, as the TIPI is a brief measure, it will eliminate item redundancy and reduce participant boredom and frustration (Gosling et al., 2003). In a study performed by Muck et al. (2007), it was established that the TIPI has psychometric properties and measurement categories suitable for use in cross–cultural research.

Whilst the results of the studies of the TIPI indicate that the measure contributes to the base of knowledge of the five-factor trait model, the message from researchers that this inventory should only be used when time is limited is very clear. Ehrhart et al. (2009) were also concerned with the alpha reliability coefficients of the study they performed using the TIPI and 50 items from the International Personality Item Pool (IPIP), which also measures the FFM. However, Gosling responds that the TIPI was not designed to meet high standards of reliability or other psychometric properties, but rather to create a brief version of the five-factor trait model of personality without sacrificing validity (Ehrhart et al., 2009).

The properties of the BTI and TIPI both show a satisfactory representation of long and short personality questionnaires. Current research on these recently developed questionnaires is quite limited. By evaluating the construct validity of the TIPI the South African-developed BTI, further evidence of the measurement of the big five personality factors can be identified.

The construct validity of the BTI and the TIPI will be examined in this study. The BTI was developed in South Africa by Taylor and De Bruin (2006) for the South African context. This questionnaire can be completed in 45 minutes and is considered to be a long personality questionnaire. The TIPI is a much shorter personality questionnaire and takes about one minute to complete. This questionnaire was developed by Gosling et al. (2003) when the need for a reliable short personality questionnaire was realised. The TIPI is therefore regarded as a short personality questionnaire. The TIPI and the BTI have both developed on the basis of the five-factor trait model, and so both measure the big five personality factors.

The BTI currently has 193 items, each in the form of a statement grouped under each of the five factors mentioned. The social desirability scale (consisting of 13 items) is placed between facets throughout the test. The BTI is presented as a single list of items. The items do not appear randomly, but instead are grouped according to their respective facets; further grouped for each factor. This format assists the respondents to better understand and contextualise the statements. There is no formal differentiation between a factor and a facet (Taylor & De Bruin, 2006).

Respondents are required to indicate to what degree they agree with a particular statement. Items are rated on a five-point Likert scale, with possible responses ranging from 1 (strongly disagree) to 5 (strongly agree). The BTI in this study was available in hard copy, and could be completed in either English or Afrikaans (Taylor & De Bruin, 2006).

The internal consistency reliability coefficients were calculated for each of the factors and facets. The reliability coefficients for the total samples were satisfactory for all the big five personality factors: Extroversion (α = 0.87), Neuroticism (α = 0.92), Conscientiousness (α = 0.93), Openness to Experience (α = 0.87) and Agreeableness (α = 0.89). With the exception of Openness to Values (α = 0.44) and Modesty (α = 0.56), the facets also had acceptable reliabilities (Taylor & De Bruin, 2006).

Interestingly, the factor analysis conducted on the BTI showed that each of the facets had a primary salient loading on the factor that they were supposed to measure, apart from Straightforwardness, which was the only facet with a secondary loading of 0.312 on Conscientiousness (See Taylor & De Bruin, 2006, for further information).

The TIPI uses a seven-point Likert scale ranging from 1 (disagree strongly) to 7 (agree strongly). There are ten items, with two descriptors per factor. Participants respond to each item by using the common stem ‘I see myself as …’. Each item has two desirable descriptors and two undesirable descriptors (e.g., for Extroversion, ‘Extroverted, enthusiastic’ and ‘Reserved, quiet’) (Woods & Hampson, 2005). The TIPI takes about one minute to complete (Gosling et al., 2003).

The psychometric properties of the TIPI can be illustrated from the scores of the correlations, test-retest reliability, and external correlates from the study by Gosling et al. (2003). According to Gosling et al., the convergent correlations (mean r = .77) exceeded the discriminant correlations (absolute mean r = .20), and none of the discriminant correlations exceeded .36. From this result it could be inferred that the TIPI measures the five factors that it claims to measure. Test-retest reliability was calculated by correlating the scores obtained in a first rating session with those obtained in a testing session completed six weeks later, and resulted in a score of r = .72.

The questionnaires were administered in hard copy and were completed during a lecture session. Completion of the questionnaire was conducted during lecture time for teaching purposes. A biographical questionnaire was administered first, followed by the two personality questionnaires. Completion of the questionnaires was carried out under standardised conditions and in accordance with the test publisher’s instructions. All the material and answer sheets were collected after the two questionnaires were completed. It was essential that all questions were answered so that the scoring process could be completed. An administrator therefore ensured that all answers were correctly marked on the answer sheet and that no items were omitted. The answer sheets were then numbered and loaded onto an SPSS data sheet and various statistical analyses were performed to obtain factors and correlations.

The multitrait-multimethod matrix is another way of establishing validity, and was used in this study. This technique assesses the construct validity of a scale. Cohen and Swerdlik (2010) noted that the construct validity of a test tending to correlate highly in the predicted direction with scores on an older, more established, and already validated, test designed to measure the same or similar construct provides evidence of convergence. Convergent evidence occurs when there are correlations between tests measuring an identical construct, and when there are correlations with a test claiming to measure related constructs. Conversely, discriminate evidence will occur if the test scores or variables do not correlate. At least two attributes, each measured by at least two methods, are required to examine discriminant validity. This data will then form a multitrait-multimethod matrix (Nunnally & Bernstein, 1994). For this study, a multitrait-multimethod matrix was implemented using the SPSS statistical programme for the five traits (Extroversion, Neuroticism, Conscientiousness, Openness and Agreeableness) that were measured using the two measuring instruments, the BTI and the TIPI.

Closer inspection of Table 2 shows that each of the BTI big five personality traits correlated most strongly with the corresponding TIPI big five personality traits (for instance, the row containing the correlations of the BTI Extroversion scale shows that its strongest correlation with a non-corresponding TIPI scale was 0.319, which is noticeably lower than its correlation of 0.581 with the corresponding TIPI Extroversion scale). Similarly, each of the TIPI big five personality traits correlated most strongly with the corresponding BTI big five personality scale (for instance, the column containing the correlations of the TIPI Extroversion scale shows that the strongest correlation with a non-corresponding BTI big five personality scale was -0.235, which is noticeably lower than its correlation of 0.581 with the corresponding BTI Extroversion scale). This pattern of correlations provides support for the convergent and discriminant validity of the scales measured by the two batteries.

FIGURE 1: The scree and parallel analysis plot.

The rotated factor pattern matrix corresponded very strongly with theoretical expectations: each of the five factors was defined by one TIPI big five personality scale and the corresponding BTI facets (see Table 3). The pattern matrix showed that factor 1 may be labelled as Extroversion, factor 2 as Neuroticism, factor 3 as Conscientiousness, factor 4 as Agreeableness and factor 5 as Openness to Experience. All the BTI facets and the TIPI scales were most strongly loaded by their expected factors, and no facet or scale was strongly loaded by unexpected factors (note, however, that Positive Affect did have a marginally salient coefficient pattern of 0.312 on the Agreeableness factor). This evidence shows that all the variables included in the analysis measured their intended factors, and none of the variables measured unintended factors.

The correlations between the five factors are given in Table 4. The largest correlation was between Extroversion and Openness to Experience (r = 0.368). With most of the correlations close to zero, it can be concluded that the factors are indeed independent of each other.

Furthermore, in the study performed by Gosling et al. (2003), Extroversion scored the highest across the criteria, and Agreeableness and Openness to Experience fared least well. Although further investigation of validity of the measure of Agreeableness is needed, the analysis suggests that the TIPI can provide a satisfactory measure of the five-factor trait model of personality constructs. It can be concluded that there is a high degree of convergence between the big five personality factors that underlie the TIPI and those that underlie the BTI.

As already mentioned, according to Friedenberg (1995), reliability is one of the psychometric properties that determine if a questionnaire is an effective test. The reliability coefficients of the BTI were satisfactory. These results imply that if the questionnaire is completed again by the same population group, the results will be consistent with the first attempt. Overall, the reliability scores of the TIPI were unsatisfactory. As this questionnaire only consists of two items per factor, it was expected that the TIPI would have lower reliability scores than the BTI. The result for the TIPI may pose concerns in terms of adherence to the requirements of South Africa’s Employment Equity Act.

The next step was to determine the correlations of the BTI facets with the TIPI big five personality factors in order to establish whether the TIPI measured the same factors as the BTI. Overall, as shown by the convergent validity correlations, each TIPI scale correlated substantially with the relevant BTI facet scales. The study yielded convergent correlations that exceeded the discriminant correlations. Inspection of the rotated pattern matrix showed that each item demonstrated convergent and discriminant validity in that each item had a salient loading on its theoretically intended factor and non-salient loadings on all the other factors.

The factor loadings on the items were relatively strong, with the exception of Extroversion and Openness to Experience. The strongest correlation of the TIPI Extroversion and the facets from the BTI were with Ascendance, Liveliness and Gregariousness. However, it is important to note that the Positive Affect BTI trait correlated on both Extroversion and Agreeableness. Although the correlation was low on both traits, the Positive Affect trait should be further explored in future studies.

All the facets of BTI Neuroticism and Conscientiousness correlated highly with TIPI Neuroticism and Conscientiousness respectively. In terms of the BTI, the facets of Openness to Experience had satisfactory ratings, with Imagination and Ideas scoring the highest correlations. The facets in the BTI Agreeableness were also satisfactory, with the Compliance facet correlating highly with the Agreeableness trait of the TIPI. Each trait appears to be unidimensional, which allows for unequivocal interpretation (with the exception of the BTI Positive Affect). The results suggest that the TIPI factors serve as good indicators of the respective BTI facets. In a similar research study, it was suggested that the TIPI short personality questionnaire should be the questionnaire of choice instead of the 44-Item BFI or the 60-item NEO-FFI. It was determined that the 44-item BFI and the 60-item NEO-FFI did not provide satisfactory facet scores for the big five personality factors when compared to the TIPI (Gosling et al., 2003).

Overall, the results of the factor analysis provided strong support for the construct validity of the two personality inventories. Whilst the results lend support that there is clear fit of the two tests with the five-factor model in terms of convergent validity. The Cronbach’s alpha coefficients of the TIPI factors ranged from 0.22 to 0.69 and were much lower than the BTI factors, which ranged from 0.90 to 0.95. These low reliabilities may reflect a degree of measurement error, and it is therefore recommended that the TIPI should be used when time is limited and only when a short measure of the big five personality factors will suffice. Conversely, the BTI showed satisfactory convergent and discriminate validity and can be regarded as a suitable measure of elements of the five-factor trait model.

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