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01.12.2012 | Research | Ausgabe 1/2012 Open Access

Health and Quality of Life Outcomes 1/2012

Psychometric Assessment of the Injection Pen Assessment Questionnaire (IPAQ): measuring ease of use and preference with injection pens for human growth hormone

Health and Quality of Life Outcomes > Ausgabe 1/2012
Andreas M Pleil, Miriam Kimel, Julie McCormack, Natasa Rajicic, Judith Hey-Hadavi
Wichtige Hinweise

Electronic supplementary material

The online version of this article (doi:10.​1186/​1477-7525-10-126) contains supplementary material, which is available to authorized users.

Competing interests

Andreas Pleil, Natasa Rajicic and Judith Hey-Hadavi are employees of Pfizer Inc. Miriam Kimel and Julie McCormack were paid consultants to Pfizer in connection with the development of this manuscript and were employed by United BioSource Corporation at the time this research was conducted. The study was funded by Pfizer, Inc., New York, NY.

Author’ contributions

AP, NR and JHH conceptualized the project and oversaw and provided scientific input regarding the development of the IPAQ. These three authors also designed and oversaw the conduct of the trial used for assessing the psychometric properties of the IPAQ. They also reviewed the statistical analysis plan (SAP) and psychometric data and provided scientific input. MK and JM designed and conducted the qualitative research and analyzed the qualitative data for developing the IPAQ as well as developed the SAP and analyzed the data for assessing the psychometric properties of the IPAQ. AP, MK, and JM also drafted the manuscript. All authors read and approved the final manuscript.



To examine the psychometric properties of the Injection Pen Assessment Questionnaire (IPAQ) including the following: 1) item and scale characteristics (e.g., frequencies, item distributions, and factor structure), 2) reliability, and 3) validity.


Focus groups and one-on-one dyad interviews guided the development of the IPAQ. The IPAQ was subsequently tested in 136 parent–child dyads in a Phase 3, 2-month, open-label, multicenter trial for a new Genotropin® disposable pen. Factor analysis was performed to inform the development of a scoring algorithm, and reliability and validity of the IPAQ were evaluated using the data from this two months study. Psychometric analyses were conducted separately for each injection pen.


Confirmatory factor analysis provides evidence supporting a second order factor solution for four subscales and a total IPAQ score. These factor analysis results support the conceptual framework developed from previous qualitative research in patient dyads using the reusable pen. However, the IPAQ subscales did not consistently meet acceptable internal consistency reliability for some group level comparisons. Cronbach’s alphas for the total IPAQ score for both pens were 0.85, exceeding acceptable levels of reliability for group comparisons.


The total IPAQ score is a useful measure for evaluating ease of use and preference for injection pens in clinical trials among patient dyads receiving hGH. The psychometric properties of the individual subscales, mainly the lower internal consistency reliability of some of the subscales and the predictive validity findings, do not support the use of subscale scores alone as a primary endpoint.
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