Intra-cluster correlation coefficients in adults with diabetes in primary care practices: the Vermont Diabetes Information System field survey

Benjamin Littenberg, Charles D MacLean, Benjamin Littenberg, Charles D MacLean

Abstract

Background: Proper estimation of sample size requirements for cluster-based studies requires estimates of the intra-cluster correlation coefficient (ICC) for the variables of interest.

Methods: We calculated the ICC for 112 variables measured as part of the Vermont Diabetes Information System, a cluster-randomized study of adults with diabetes from 73 primary care practices (the clusters) in Vermont and surrounding areas.

Results: ICCs varied widely around a median value of 0.0185 (Inter-quartile range: 0.006, 0.037). Some characteristics (such as the proportion having a recent creatinine measurement) were highly associated with the practice (ICC = 0.288), while others (prevalence of some comorbidities and complications and certain aspects of quality of life) varied much more across patients with only small correlation within practices (ICC<0.001).

Conclusion: The ICC values reported here may be useful in designing future studies that use clustered sampling from primary care practices.

References

    1. Kerry SM, Bland JM. Analysis of a trial randomized in clusters. BMJ. 1998;316:54.
    1. Kerry SM, Bland JM. The intracluster correlation coefficient in cluster randomization. BMJ. 1998;316:1455.
    1. Knox SA, Chondros P. Observed intra-cluster correlation coefficients in a cluster survey sample of patient encounters in general practice in Australia. BMC Medical Research Methodology. 2004;4:30. doi: 10.1186/1471-2288-4-30.
    1. Smeeth L, Ng ES. Intraclass correlation coefficients for cluster randomized trials in primary care: data from the MRC Trial of the Assessment and Management of Older People in the Community. Controlled Clinical Trials. 2002;23:409–21. doi: 10.1016/S0197-2456(02)00208-8.
    1. Parker DR, Evangelou E, Eaton CB. Intraclass correlation coefficients for cluster randomized trials in primary care: the cholesterol education and research trial (CEART) Contemporary Clinical Trials. 2005;26:260–7. doi: 10.1016/j.cct.2005.01.002.
    1. Elley CR, Kerse N, Chondros P, Robinson E. Intraclass correlation coefficients from three cluster randomised trials in primary and residential care. Aust N Z J Public Health. 2005;29:461–467.
    1. MacLean CD, Littenberg B, Gagnon M, Reardon M, Turner P, Jordan C. The Vermont Diabetes Information System (VDIS): study design and subject recruitment for a cluster randomized trial of a diabetes registry in a statewide sample of primary care practices. Clinical Trials. 2004;1:532–544. doi: 10.1191/1740774504cn051oa.
    1. Strauss K, MacLean CD, Troy AR, Littenberg B. Driving distance as a barrier to glycemic control in diabetes. J Gen Intern Med. 2006;21:378–80. doi: 10.1111/j.1525-1497.2006.00386.x.
    1. Friedwald WT, Levy RI, Frederickson DS. Estimation of the concentration of low density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifugation. Clin Chem. 1972;18:499–502.
    1. American Diabetes Association Clinical Practice Recommendations. Diabetes Care. 2005;28
    1. Vermont Program for Quality in Health Care . Recommendations for management of Diabetes in Vermont. Montpelier: Vermont Program for Quality in Health Care; 2004.
    1. Ewing JA. Detecting Alcoholism: The CAGE Questionnaire. JAMA. 1984;252:1905–1907. doi: 10.1001/jama.252.14.1905.
    1. Toobert DJ, Hampson SE, Glasgow RE. The summary of diabetes self-care activities measure: results from 7 studies and a revised scale. Diabetes Care. 2000;23:943–50.
    1. Parker RM, Baker DW, Williams MV, Nurss JR. The test of functional health literacy in adults: a new instrument for measuring patients' literacy skills. J Gen Intern Med. 1995;10:537–41.
    1. Baker DW, Williams MV, Parker RM, Gazmararian JA, Nurss J. Development of a brief test to measure functional health literacy. Patient Educ Couns. 1999;38:33–42. doi: 10.1016/S0738-3991(98)00116-5.
    1. Katz JN, Chang LC, Sangha O, Fossel AH, Bates DW. Can comorbidity be measured by questionnaire rather than medical record review? Med Care. 1996;34:73–84. doi: 10.1097/00005650-199601000-00006.
    1. Sangha O, Stucki G, Liang MH, Fossel AH, Katz JN. The Self-Administered Comorbidity Questionnaire: a new method to assess comorbidity for clinical and health services research. Arthritis Rheum. 2003;49:156–63. doi: 10.1002/art.10993.
    1. Ware JE, Kosinski M, Turner-Bowker DM, Gandek B. How to Score Version 2 of the SF-12 Health Survey. Lincoln, RI: Quality Metric Inc; 2002.
    1. Kroenke K, Spitzer RL, Williams JB. The PHQ-9: validity of a brief depression severity measure. J Gen Intern Med. 2001;16:606–13. doi: 10.1046/j.1525-1497.2001.016009606.x.
    1. Bradley C, Todd C, Gorton T, Symonds E, Martin A, Plowright R. The development of an individualized questionnaire measure of perceived impact of diabetes on quality of life: the ADDQoL. Qual Life Res. 1999;8:79–91. doi: 10.1023/A:1026485130100.
    1. Bradley C, Speight J. Patient perceptions of diabetes and diabetes therapy: assessing quality of life. Diabetes Metab Res Rev. 2002;18:S64–9. doi: 10.1002/dmrr.279.
    1. Stata Corporation . Stata Base Reference Manual, G-M, Release 8. Vol. 2. College Station, TX: Stata Press; 2003. Loneway – Large one-way ANOVA random effects, and reliabaility; pp. 338–43.
    1. Gleason JR. Computing intraclass correlations and large ANOVAs. Stata Technical Bulletin. 1997;35:25–31.
    1. Donner A. A review of inference procedures for the intraclass correlation coefficient in the one-way random effects model. International Statistical Review. 1986;54:67–82.
    1. Gulliford MC, Adams G, Ukoumunne OC, Latinovic R, Chinn S, Campbell MJ. Intraclass correlation coefficient and outcome prevalence are associated in clustered binary data. Journal of Clinical Epidemiology. 2005;58:246–251. doi: 10.1016/j.jclinepi.2004.08.012.
    1. Cohen J. Statistical power analysis for the behavioral sciences. 2. Hillsdale, NJ : Lawrence Erlbaum Associates; 1988.
    1. Campbell MK, Fayers PM, Grimshaw JM. Determinants of the intracluster correlation coefficient in cluster randomized trials: the case of implementation research. Clin Trials. 2005;2:99–107. doi: 10.1191/1740774505cn071oa.
    1. Adams G, Gulliford MC, Ukoumunne OC, Eldridge S, Chinn S, Campbell MJ. Patterns of intra-cluster correlation from primary care research to inform study design and analysis. Journal of Clinical Epidemiology. 2004;57:785–794. doi: 10.1016/j.jclinepi.2003.12.013.

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