On the validity of measuring change over time in routine clinical assessment: a close examination of item-level response shifts in psychosomatic inpatients.
Significant life events such as severe health status changes or intensive medical treatment often trigger response shifts in individuals that may hamper the comparison of measurements over time. Drawing from the Oort model, this study aims at detecting response shift at the item level in psychosomatic inpatients and evaluating its impact on the validity of comparing repeated measurements.



Complete pretest and posttest data were available from 1188 patients who had filled out the ICD-10 Symptom Rating (ISR) scale at admission and discharge, on average 24 days after intake. Reconceptualization, reprioritization, and recalibration response shifts were explored applying tests of measurement invariance. In the item-level approach, all model parameters were constrained to be equal between pretest and posttest. If non-invariance was detected, these were linked to the different types of response shift.



When constraining across-occasion model parameters, model fit worsened as indicated by a significant Satorra-Bentler Chi-square difference test suggesting potential presence of response shifts. A close examination revealed presence of two types of response shift, i.e., (non)uniform recalibration and both higher- and lower-level reconceptualization response shifts leading to four model adjustments.



Our analyses suggest that psychosomatic inpatients experienced some response shifts during their hospital stay. According to the hierarchy of measurement invariance, however, only one of the detected non-invariances is critical for unbiased mean comparisons over time, which did not have a substantial impact on estimating change. Hence, the use of the ISR can be recommended for outcomes assessment in clinical routine, as change score estimates do not seem hampered by response shift effects.
Department of Psychosomatic Medicine, Center for Internal Medicine and Dermatology, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117, Berlin, Germany. sandra.nolte@charite.de.|Population Health Strategic Research Centre, School of Health and Social Development, Deakin University, Burwood, VIC, 3125, Australia. sandra.nolte@charite.de.
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0000-0001-6185-9423
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Nolte
Department of Psychosomatic Medicine, Center for Internal Medicine and Dermatology, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117, Berlin, Germany.
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Mierke
Department of Psychosomatic Medicine, Center for Internal Medicine and Dermatology, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117, Berlin, Germany.|Institute for Social Medicine, Epidemiology and Health Economics, Charité - Universitätsmedizin Berlin, Berlin, Germany.
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Fischer
Department of Psychosomatic Medicine, Center for Internal Medicine and Dermatology, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117, Berlin, Germany.|Quantitative Health Sciences, Outcomes Measurement Science, University of Massachusetts Medical School, Worcester, MA, USA.
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Rose
D005260:Female; D006304:Health Status; D006801:Humans; D007297:Inpatients / Q000523:psychology*; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D011602:Psychophysiologic Disorders / Q000523:psychology*; D011788:Quality of Life / Q000523:psychology*; D015203:Reproducibility of Results; D018434:Sickness Impact Profile; D013997:Time Factors
Evaluation; Measurement bias; Measurement invariance; Psychosomatic medicine; Response shift; Routine monitoring