Assessing Measurement Invariance of the Diabetes Stress Questionnaire in Youth With Type 1 Diabetes Rebecca C. Kamody,1 BS, Kristoffer S. Berlin,1,2 PHD, Anthony A. Hains,3 PHD, Jessica C. Kichler,4 PHD, CDE, W. Hobart Davies,5 PHD, Alicia M. Diaz-Thomas,2,6 MD, MPH, and Robert J. Ferry, Jr.,2 MD, FAAP 1
Department of Psychology, The University of Memphis, 2Department of Pediatrics, University of Tennessee
Health Science Center, 3Department of Educational Psychology, University of Wisconsin-Milwaukee, Cincinnati Children’s Hospital Medical Center, 5Department of Psychology, University of Wisconsin-
Milwaukee, and 6LeBonheur Children’s Hospital
All correspondence concerning this article should be addressed to Rebecca C. Kamody, BS, Department of Psychology, The University of Memphis, Memphis, TN 38152, USA. E-mail: [email protected] Received April 22, 2014; revisions received August 15, 2014; accepted August 17, 2014 Objective To evaluate the factor structure and measurement invariance of the Diabetes Stress Questionnaire (DSQ), a measure of diabetes-specific stress, across sex, age (15,000 new cases diagnosed every year (American Diabetes Association [ADA], 2013a; Centers for Disease Control and Prevention [CDC], 2013). If not managed properly, glycemic control will be affected, resulting in serious complications, including, but not limited to, heart disease, stroke, neuropathy, nephropathy, glaucoma, diabetic ketoacidosis, and death (ADA, 2013b). Risks of diabetes complications are reduced by following an intensive regimen, which requires individuals to monitor their diet, exercise regularly, test blood sugar levels numerous times per day, and either administer multiple insulin injections or use an insulin pump to adhere to a basal/bolus insulin regimen (National Diabetes Information
Clearinghouse, 2014; Silverstein et al., 2005). Although diabetes management can be difficult at any age, it can be particularly challenging for adolescents with T1D (Greening, Stoppelbein, Konishi, Jordan, & Moll, 2007). Multiple interacting factors influence diabetes outcomes such as glycemic control and quality of life, including access to medical care, parent education and involvement, and demographic characteristics (i.e., sex, age, etc.), among many others (Franklin et al., 2014; Naughton et al., 2014; Valenzuela et al., 2014). One explanation for the difficulties that adolescents experience with their diabetes management is the role of diabetesspecific stress (Malik & Koot, 2009; Smith et al., 2013). Based on Baum’s (1990) general definition of stress, diabetes-specific stress is defined here as a typically
Journal of Pediatric Psychology 39(10) pp. 1138–1148, 2014 doi:10.1093/jpepsy/jsu076 Advance Access publication September 23, 2014 Journal of Pediatric Psychology vol. 39 no. 10 ß The Author 2014. Published by Oxford University Press on behalf of the Society of Pediatric Psychology. All rights reserved. For permissions, please e-mail: [email protected]
Downloaded from http://jpepsy.oxfordjournals.org/ at University of North Carolina at Greensboro on November 9, 2014
4
Measurement Invariance of the DSQ
2012) has been applied frequently in research and clinical settings to assess multiple types of diabetes-specific stressors and the contexts in which they occur (e.g., family, school, peers; Berlin et al., 2012; Delamater et al., 2012; Hains et al., 2006, 2007, 2009; Silverman, Hains, Davies, & Parton, 2003). One common usage of the DSQ is to explore how diabetes-specific stress functions differently across groups (i.e., male vs. female; younger vs. older youth). This research question assumes that the constructs measured by the DSQ are the same across these different groups being compared; however, this assumption has yet to be tested. It is important that the measure is statistically invariant across such groups to ensure that the measure is functioning the same way (Millsap, 2011). Therefore, any differences when comparing group means, correlations, and path coefficients can be attributed to actual differences between the groups. Without testing for invariance, parameter differences between the groups could be explained by differences in how the assessment instrument is measuring the construct, or how individuals are responding to various items, and renders any group differences equivocal. By ensuring invariance of the DSQ, any group differences found in future research using the measure can be reliably assumed to result from actual differences between groups, and not simply artifacts of measurement differences across these different groups. Additionally, the DSQ may qualify as an evidence-based assessment (Holmbeck et al., 2008; Quittner, Modi, Lemanek, Ievers-Landis, & Rapoff, 2008), pending further exploration of the DSQ’s psychometric properties. The purpose of the present study is to first confirm the factor structure of the DSQ (Delamater et al., 2012) and then determine the extent to which the DSQ demonstrates measurement invariance across biological sex, age (14.0%) Suboptimal HbA1c Optimal HbA1c N/A Total
241
75.8
72
22.6
5
1.6
318
Age distribution (years) 8
1
0.3
10 11
2 34
0.6 10.7
12
49
15.4
13
65
20.4
14
47
14.8
15
41
12.9
16
36
11.3
17
34
10.7
9 318
2.8
249
78.3
47
14.8
Latino(a) American
5
1.6
Asian American
3
0.9
Native American
3
0.9
Biracial N/A
7 4
2.2 1.3
18 Total Race/ethnicity White/European American African American
Total
318
control’’); the Peer Stress factor is composed of eight items (e.g., ‘‘Testing my blood when friends are with me’’); the Averse Interpersonal Effects factor is composed of nine items (e.g., ‘‘Feeling that people treat me differently because they know I have diabetes’’); the Parental Stress factor is composed of seven items (e.g., ‘‘My parents reminding or nagging me about testing my blood or urine’’); the Hyperglycemia factor is composed of eight items (e.g., ‘‘Being in the hospital for ketoacidosis’’); the Self-Care Regimen factor is composed of eight items (e.g., ‘‘Writing down the results of blood and urine tests; keeping good records’’); the Diet factor is composed five items (e.g., ‘‘Not being able to eat foods that my friends can eat’’);
Downloaded from http://jpepsy.oxfordjournals.org/ at University of North Carolina at Greensboro on November 9, 2014
Data from the PRYDE study participants were collected at a pediatric diabetes clinic, and institutional review board (IRB) approval was obtained from the necessary respective medical facility and university where the data were collected. Eligible participants
Department of Psychology, The University of Memphis, 2Department of Pediatrics, University of Tennessee
Health Science Center, 3Department of Educational Psychology, University of Wisconsin-Milwaukee, Cincinnati Children’s Hospital Medical Center, 5Department of Psychology, University of Wisconsin-
Milwaukee, and 6LeBonheur Children’s Hospital
All correspondence concerning this article should be addressed to Rebecca C. Kamody, BS, Department of Psychology, The University of Memphis, Memphis, TN 38152, USA. E-mail: [email protected] Received April 22, 2014; revisions received August 15, 2014; accepted August 17, 2014 Objective To evaluate the factor structure and measurement invariance of the Diabetes Stress Questionnaire (DSQ), a measure of diabetes-specific stress, across sex, age (15,000 new cases diagnosed every year (American Diabetes Association [ADA], 2013a; Centers for Disease Control and Prevention [CDC], 2013). If not managed properly, glycemic control will be affected, resulting in serious complications, including, but not limited to, heart disease, stroke, neuropathy, nephropathy, glaucoma, diabetic ketoacidosis, and death (ADA, 2013b). Risks of diabetes complications are reduced by following an intensive regimen, which requires individuals to monitor their diet, exercise regularly, test blood sugar levels numerous times per day, and either administer multiple insulin injections or use an insulin pump to adhere to a basal/bolus insulin regimen (National Diabetes Information
Clearinghouse, 2014; Silverstein et al., 2005). Although diabetes management can be difficult at any age, it can be particularly challenging for adolescents with T1D (Greening, Stoppelbein, Konishi, Jordan, & Moll, 2007). Multiple interacting factors influence diabetes outcomes such as glycemic control and quality of life, including access to medical care, parent education and involvement, and demographic characteristics (i.e., sex, age, etc.), among many others (Franklin et al., 2014; Naughton et al., 2014; Valenzuela et al., 2014). One explanation for the difficulties that adolescents experience with their diabetes management is the role of diabetesspecific stress (Malik & Koot, 2009; Smith et al., 2013). Based on Baum’s (1990) general definition of stress, diabetes-specific stress is defined here as a typically
Journal of Pediatric Psychology 39(10) pp. 1138–1148, 2014 doi:10.1093/jpepsy/jsu076 Advance Access publication September 23, 2014 Journal of Pediatric Psychology vol. 39 no. 10 ß The Author 2014. Published by Oxford University Press on behalf of the Society of Pediatric Psychology. All rights reserved. For permissions, please e-mail: [email protected]
Downloaded from http://jpepsy.oxfordjournals.org/ at University of North Carolina at Greensboro on November 9, 2014
4
Measurement Invariance of the DSQ
2012) has been applied frequently in research and clinical settings to assess multiple types of diabetes-specific stressors and the contexts in which they occur (e.g., family, school, peers; Berlin et al., 2012; Delamater et al., 2012; Hains et al., 2006, 2007, 2009; Silverman, Hains, Davies, & Parton, 2003). One common usage of the DSQ is to explore how diabetes-specific stress functions differently across groups (i.e., male vs. female; younger vs. older youth). This research question assumes that the constructs measured by the DSQ are the same across these different groups being compared; however, this assumption has yet to be tested. It is important that the measure is statistically invariant across such groups to ensure that the measure is functioning the same way (Millsap, 2011). Therefore, any differences when comparing group means, correlations, and path coefficients can be attributed to actual differences between the groups. Without testing for invariance, parameter differences between the groups could be explained by differences in how the assessment instrument is measuring the construct, or how individuals are responding to various items, and renders any group differences equivocal. By ensuring invariance of the DSQ, any group differences found in future research using the measure can be reliably assumed to result from actual differences between groups, and not simply artifacts of measurement differences across these different groups. Additionally, the DSQ may qualify as an evidence-based assessment (Holmbeck et al., 2008; Quittner, Modi, Lemanek, Ievers-Landis, & Rapoff, 2008), pending further exploration of the DSQ’s psychometric properties. The purpose of the present study is to first confirm the factor structure of the DSQ (Delamater et al., 2012) and then determine the extent to which the DSQ demonstrates measurement invariance across biological sex, age (14.0%) Suboptimal HbA1c Optimal HbA1c N/A Total
241
75.8
72
22.6
5
1.6
318
Age distribution (years) 8
1
0.3
10 11
2 34
0.6 10.7
12
49
15.4
13
65
20.4
14
47
14.8
15
41
12.9
16
36
11.3
17
34
10.7
9 318
2.8
249
78.3
47
14.8
Latino(a) American
5
1.6
Asian American
3
0.9
Native American
3
0.9
Biracial N/A
7 4
2.2 1.3
18 Total Race/ethnicity White/European American African American
Total
318
control’’); the Peer Stress factor is composed of eight items (e.g., ‘‘Testing my blood when friends are with me’’); the Averse Interpersonal Effects factor is composed of nine items (e.g., ‘‘Feeling that people treat me differently because they know I have diabetes’’); the Parental Stress factor is composed of seven items (e.g., ‘‘My parents reminding or nagging me about testing my blood or urine’’); the Hyperglycemia factor is composed of eight items (e.g., ‘‘Being in the hospital for ketoacidosis’’); the Self-Care Regimen factor is composed of eight items (e.g., ‘‘Writing down the results of blood and urine tests; keeping good records’’); the Diet factor is composed five items (e.g., ‘‘Not being able to eat foods that my friends can eat’’);
Downloaded from http://jpepsy.oxfordjournals.org/ at University of North Carolina at Greensboro on November 9, 2014
Data from the PRYDE study participants were collected at a pediatric diabetes clinic, and institutional review board (IRB) approval was obtained from the necessary respective medical facility and university where the data were collected. Eligible participants
