Rasch Model Analysis Spss Manual

Rasch model analysis spss manual

However, CTT has a major disadvantage of invalid summated score, and using Rasch models can overcome the shortcoming. Parallel analysis PA and Rasch rating scale models were used for statistical analyses.

Rasch model analysis spss manual

The Rasch analyses showed three negatively worded items 2 in Physical and 1 in Psychological reported as misfits that may not contribute to the Physical and Psychological domains; one positively worded item in the Physical domain may be redundant. All values for the separation indices were above 2 except for the person separation index in the Physical domain 1. It can also be used as a treatment outcome measure to evaluate the effect of treatments for substance abusers.

However, the three misfit negatively worded items should be used with caution because the substance abuser may not fully understand their meaning. Future research may apply cognitive interviews to determine the cognitive functioning of substance abusers and their interpretation of negatively worded items.

Substance abuse, such as heroin addiction, may cause economic burdens for individual users and for the society as a whole [ 1 , 2 ].

Substance abusers are likely to have comorbid infectious diseases, for example, the human immunodeficiency virus HIV , hepatitis B virus HBV , and hepatitis C virus HCV , because of needle sharing [ 3 ]. Therefore, substance abusers may have physically and mentally multiple negative consequences as well as those applicable to their social relationships [ 4 ], and they are reported to have a poorer quality of life QoL than those who are not substance-dependent [ 5 ].

QoL is used as an important outcome measure for healthcare decision-making and for evaluating intervention effects [ 6 , 7 ], such as the effect of medicine [ 8 ], and studies e. Specifically, CTT methods treat raw scores and item responses to rating scales as interval data, and this may yield invalid scores.


Therefore, there is a trend toward using Rasch analysis, a modern statistical method that can transform the ordinal scores of polytomous items into interval scores for the purpose of psychometric evaluation [ 16 ]. Although Rasch models have the main weakness of being a complicated model theory in terms of mathematical equations that are hard for clinicians to understand [ 17 ], it has the following strengths: 1 the validity of the items can be individually analyzed to determine any redundancy, which may not be detected by CTT; 2 item difficulty can be estimated; 3 an ordinal-to-interval conversion table can be produced that can help clinicians use the items to understand the latent traits of respondents [ 18 - 20 ].

Rasch model analysis spss manual

In addition, a number of ordered polytomous Rasch models, such as the partial credit model PCM and the rating scale model RSM , have been used in QoL instruments that are rated on a Likert scale [ 18 ].

Because Rasch models can detect items that are out-of-concept or redundant and can precisely measure the latent QoL of a heroin user using an ordinal-to-interval conversion table, the purpose of this study was to use several Rasch models to examine the psychometric properties of the WHOQOL-BREF in a heroin-dependent sample in Taiwan.

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Of the 28 items, 2 are generic items that test overall QoL and general health i. Domain score calculation has been reported elsewhere [ 13 ], and potential scores for each domain ranged from 4 to 20, with a higher score representing a better QoL.

Reversely coded items are in italics ; misfit values are in bold. Descriptive analyses yielding means, standard deviations SDs , and frequencies were used to determine the characteristics of the participants. A major assumption of the Rasch model is unidimensionality for each domain [ 17 , 18 ].

PA was used to produce simulation results, and these simulation results were compared to the results from our participants. The number of dimensions was decided based on how many extracted factors had an eigenvalue greater than the generated mean eigenvalue and estimated eigenvalue at the 95th percentile. For example, if the Physical domain has 2 extracted factors with eigenvalues greater than the generated mean eigenvalue and estimated eigenvalue at the 95th percentile, the Physical domain is determined to be 2-dimensional.

Therefore, the 2 generic items were not examined in this study. Two fit indices information-weighted fit statistic [infit] mean square [MnSq] and outlier-sensitive fit statistic [outfit] MnSq were used, and the MnSq range of 0.

Introduction to Rasch Analysis using RUMM2030

The Rasch rating-scale model can report standardized item difficulties with a mean of 0 and an SD of 1 log-odd unit i. A higher logit represents a more difficult item. Item and person separation reliability, separation index, category functioning, local dependency, and person fit statistics have also been assessed using Rasch RSM models.

Rasch model analysis spss manual

Person separation reliability was measured by the reproducibility of person ordering on respondent abilities when they answer another set of items measuring the same concept, while item separation reliability was evaluated by the reproducibility of hierarchical item difficulty when the same items were answered by another set of respondents with comparable ability. We applied separation indices to examine how well the respondents can be discriminated person separation index and by how well the items can be separated item separation index using questionnaires [ 18 ].

Both average and step measures are expected to monotonically increase with categories, while both fit statistics are recommended to be between 0. Local dependency, which means that some items are still correlated after the same underlying concept has been taken into account e. If there is no local dependency, the r will be 0; however, Wang et al.

Using the person fit statistics, the person response validity can be examined for logical hierarchical ordering [ 27 ].

Rasch Model / Rasch Analysis: Definition, Examples

Fisher et al. However, we decided not to adopt such a criterion, and simply reported the percentage of misfit respondents because our sample had a special mental health issue. Finally, items were tested for differential item functioning DIF across educational level junior high vs. The mean SD age of the participants was Their mean duration of heroin use was 8.

In addition, The PA showed that only the first factor extracted from each domain had a higher observed eigenvalue as compared to the estimated eigenvalue at the 95th percentile. In addition, the second factor extracted from the Physical domain had the same value 1. Because each domain was found to be unidimensional, further Rasch analyses were appropriate. Therefore, the thresholds of the 5 categories followed the expected order. Correlation coefficients of residuals between items for Item dependency tests.

Differential item functioning DIF items detected across different groups. Unidimensionality of the Social and Environment domains was evidenced using both PA and Rasch models; however, the Physical and Psychological domains had misfit items. Three items Ph1, Ph2, and Ps6 were not embedded in their underlying domain, and item Ph6 was redundant.

No disordering was detected for 5 thresholds in the four domains, and item dependency was acceptable.

Statistics for the rest of us!

However, about one-fifth of the subjects were found to be misfit, possibly indicating the unstable nature of heroin users. Our results of the satisfactory reliability Physical: 0.

In addition, we extended the satisfactory reliability to the acceptable separation index. However, we found that some misfit items in the Physical and Psychological domains contradicted previous Rasch model findings [ 13 , 16 , 29 ].

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One possible reason for this is the different populations used between our study and previous studies substance abusers vs. Substance abusers are often cognitively impaired [ 30 ], and thus may have difficulty understanding some items that use indirect wordings e.

Because three misfit items in this study were negatively worded, we tentatively concluded that substance abusers may not have sufficient intact cognitive function to interpret the three items as they were intended to be understood. Negatively worded items have a wording effect that biases the evaluation of the extracting constructs of QoL instruments [ 31 ], especially in the case of people without sufficient cognitive ability.

Therefore, the underlying constructs, such as the Physical and Psychological domains, may be affected by the negatively worded items [ 32 , 33 ]. In order to strengthen our hypothesis i.


Two CFA models M1: 4-QoL-factor model, and M2: correlated QoL traits and uncorrelated wording methods were compared, and we hypothesized that M2 outperformed M1 because it includes the wording effect in the model. The CFA results, therefore, somewhat confirmed our hypothesis. However, because no cognitive tests were done in this study, our hypothesis was only supported by indirect evidence i. Therefore, future researchers may want to verify our hypothesis using direct investigations.

For example, cognitive interviews can be conducted to clarify whether substance abusers have insufficient cognitive functioning by which to understand negatively worded items. In addition, DIF analyses among substance abusers and non-abusers on negatively worded items may also justify our hypothesis. The major reasons for this may be a combination of following factors: excellent instruction documents originally provided by the WHOQOL team for the establishment of the version for Taiwan, sound leadership and cooperation among psychometricians, clinicians, and statisticians in Taiwan to form a focus group for the development, careful selection of descriptors for each item [ 34 ], standard translation procedure i.

Future studies are warranted for corroboration of our findings in people with other mental illnesses.

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A substantial percentage Because we assessed subject reported outcomes from patients, which are frequently affected by emotion and cognition [ 35 , 36 ], less than one-quarter of person misfit may indeed be acceptable. However, more studies are needed to corroborate our speculation. In addition, we found one DIF item for educational level and another one for gender. The participants with less than a junior high school education seemed to overestimate eating satisfaction, or they seemed to be more easily satisfied than those with higher education and thus to report a higher score on item E9.

Furthermore, the reason that females report an underestimated sexual life QoL may be due to their embarrassment or higher expectations. This study has three main limitations.

First, all participants were recruited in the same MMT program in southern Taiwan, which prevents us from generalizing our results to the entire Taiwanese population. Therefore, the generalizability issue may not be serious. Second, the participants were recruited from an MMT program; thus, our results may not be applicable to substance abusers who do not seek anti-addiction treatment.

Third, all participants in this study used heroin, and only some used other substances e.

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Therefore, our results may be more representative of the heroin-dependent population and less representative of populations dependent upon other substances. However, those with and without HIV infection should be interpreted after stratification, and the three negatively worded items should be used with caution because substance abusers may have cognitive problems that may preclude them from having a full understanding of the meanings. Competing interests. The authors declare that there are no conflicts of interests and that the agency that funded this research was not involved in the study design, data analysis, data interpretation, or writing of the report.

Rasch model analysis spss manual

K-CC conceptualized and designed the study, interpreted the data, and revised the manuscript. J-DW designed the study, interpreted the data, and revised the manuscript.

C-YL acquired and analyzed the data and drafted the manuscript. All of the authors revised the manuscript and approved the final manuscript.

Multiple-Choice, Rating Scale and Partial Credit Rasch Analysis

Kun-Chia Chang, Email: wt. Jung-Der Wang, Email: moc. Hsin-Pei Tang, Email: moc. Ching-Ming Cheng, Email: moc.

What is a Rasch Model?

Chung-Ying Lin, Email: wt. National Center for Biotechnology Information , U. Health Qual Life Outcomes. Published online Oct 3. Author information Article notes Copyright and License information Disclaimer. Corresponding author. Received May 30; Accepted Sep This article has been cited by other articles in PMC.

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