An Evaluation of the Psychometric Properties of the STPI (Form Y) for South African Students
Year: 2014
Type: dissertation
Abstract: This study investigated the psychometric properties of the State Trait Personality \nInventory (STPI-Y) with a South African student sample. Both classical test theory and \nitem response theory (Rasch Model) were used. The sample comprised 2298 students. \nThe students ranged in age from 17 years to 51 years. \nThe reliability of the STPI-Y was evaluated using both the Cronbach’s alpha internal \nconsistency reliability and the person and item separation indices obtained using Rasch \nanalysis. The Cronbach’s alpha reliability coefficient for all eight scales ranged from \nsatisfactory (.72) to excellent (.92). The person separation indices were mostly below .80, \nwhich indicates that more items need to be added to these scales to adequately distinguish \nbetween those with higher levels and those with lower levels of each state or trait. The \nitem separation indices were generally above .90, indicating that the sample was large \nenough to confirm the hierarchy of item difficulties. \nRasch analysis of the fit of the different scales of the STPI-Y indicated that two items \non the State Curiosity scale and one item on the Trait Curiosity scale appear to measure a \ndifferent dimension from the remaining items on each scale. Exploratory and \nconfirmatory factor analysis also indicated that certain items on the State Curiosity and \nTrait Curiosity scales had poor factor loadings. These findings are consistent with \nprevious research studies. \nNonparametric statistics were used to determine if differences existed between gender \nand ethnic groups. With the exception of the Trait Anger scale, statistically significant \nmedian differences between the gender groups were reported on each of the scales of the \nSTPI-Y. Statistically significant differences were also found when comparing ethnic group medians. The effect sizes of these differences, however, were below .10 and are \nunlikely to impact the interpretation of the scores across the groups. \nUniform differential item functioning (DIF) was used to explore possible bias \nbetween gender and ethnic groups. There was minimal evidence of DIF when comparing \ngender groups. When comparing ethnic groups, there was little evidence of DIF on the \nState and Trait Curiosity scales. Differences on the remaining scales were across different \nethnic groups and in different directions, therefore, it was concluded that these results are \nunlikely to result in bias at scale level. \nThe suitability of the language of the STPI-Y items was also investigated. Some items \nwere found to be problematic. However, if these items were deleted, little change would \noccur in the reliability of their scales. \nIt appears that the STPI-Y scales have acceptable psychometric properties for the \nSouth African student population. However, the State and Trait Curiosity subscales need \nto be interpreted with caution. It is recommended that the tool is constantly refined and \nresearched to continually improve the quality of the instrument.
Authors: Du Plessis, Kathrine Emma
Language: English
Field: Decision Sciences
Domain: Social Sciences
Open Access status: green
OpenAlex ID: W583237893