Intracluster correlation coefficients for sample size calculations related to cardiovascular disease prevention and management in primary care practices

Jatinderpreet Singh, Clare Liddy, William Hogg, Monica Taljaard, Jatinderpreet Singh, Clare Liddy, William Hogg, Monica Taljaard

Abstract

Background: Few studies have comprehensively reported intracluster correlation coefficient (ICC) estimates for outcomes collected in primary care settings. Using data from a large primary care study, we aimed to: a) report ICCs for process-of-care and clinical outcome measures related to cardiovascular disease management and prevention, and b) investigate the impact of practice structure and rurality on ICC estimates.

Methods: We used baseline data from the Improved Delivery of Cardiovascular Care (IDOCC) trial to estimate ICC values. Data on 5,140 patients from 84 primary care practices across Eastern Ontario, Canada were collected through chart abstraction. ICC estimates were calculated using an ANOVA approach and were calculated for all patients and separately for patient subgroups defined by condition (i.e., coronary artery disease, diabetes, chronic kidney disease, hypertension, dyslipidemia, and smoking). We compared ICC estimates between practices in which data were collected from a single physician versus those that had multiple participating physicians and between urban versus rural practices.

Results: ICC estimates ranged from 0 to 0.173, with a median of 0.056. The median ICC estimate for dichotomous process outcomes (0.088) was higher than that for continuous clinical outcomes (0.035). ICC estimates calculated for single physician practices were higher than those for practices with multiple physicians for both process (average 3.9-times higher) and clinical measures (average 1.9-times higher). Urban practices tended to have higher process-of-care ICC estimates than rural practices, particularly for measuring lipid profiles and estimated glomerular filtration rates.

Conclusion: To our knowledge, this is the most comprehensive summary of cardiovascular-related ICCs to be reported from Canadian primary care practices. Differences in ICC estimates based on practice structure and location highlight the importance of understanding the context in which external ICC estimates were determined prior to their use in sample size calculations. Failure to choose appropriate ICC estimates can have substantial implications for the design of a cluster randomized trial.

References

    1. Eldridge SM, Ashby D, Feder GS, Rudnicka AR, Ukoumunne OC. Lessons for cluster randomized trials in the twenty-first century: a systematic review of trials in primary care. Clin Trials. 2004;1:80–90. doi: 10.1191/1740774504cn006rr.
    1. Donner A, Klar N. Design and Analysis of Cluster Randomization Trials in Health Research. London: Arnold Publishers; 2000.
    1. Cornfield J. Randomization by group: a formal analysis. Am J Epidemiol. 1978;108:100–2.
    1. Campbell MK, Thomson S, Ramsay CR, MacLennan GS, Grimshaw JM. Sample size calculator for cluster randomized trials. Comput Biol Med. 2004;34:113–25. doi: 10.1016/S0010-4825(03)00039-8.
    1. Hayes RJ, Bennett S. Simple sample size calculation for cluster-randomized trials. Int J Epidemiol. 1999;28:319–26. doi: 10.1093/ije/28.2.319.
    1. Hemming K, Girling AJ, Sitch AJ, Marsh J, Lilford RJ. Sample size calculations for cluster randomised controlled trials with a fixed number of clusters. BMC Med Res Methodol. 2011;11:102. doi: 10.1186/1471-2288-11-102.
    1. Donner A, Birkett N, Buck C. Randomization by cluster sample size requirements and analysis. Am J Epidemiol. 1981;114:906–14.
    1. Campbell MK, Piaggio G, Elbourne DR, Altman DG. Consort 2010 statement: extension to cluster randomised trials. BMJ. 2012;345:e5661. doi: 10.1136/bmj.e5661.
    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. J Clin Epidemiol. 2004;57:785–94. doi: 10.1016/j.jclinepi.2003.12.013.
    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. Gulliford MC, Adams G, Ukoumunne OC, Latinovic R, Chinn S, Campbell MJ. Intraclass correlation coefficient and outcome prevalence are associated in clustered binary data. J Clin Epidemiol. 2005;58:246–51. doi: 10.1016/j.jclinepi.2004.08.012.
    1. Murray DM, Short B. Intraclass correlation among measures related to alcohol use by young adults: estimates, correlates and applications in intervention studies. J Stud Alcohol. 1995;56:681–94. doi: 10.15288/jsa.1995.56.681.
    1. Liddy C, Hogg W, Russell G, Wells G, Armstrong CD, Akbari A, et al. Improved delivery of cardiovascular care (IDOCC) through outreach facilitation: study protocol and implementation details of a cluster randomized controlled trial in primary care. Implement Sci. 2011;6:110. doi: 10.1186/1748-5908-6-110.
    1. Littenberg B, MacLean CD. Intra-cluster correlation coefficients in adults with diabetes in primary care practices: the Vermont Diabetes Information System field survey. BMC Med Res Methodol. 2006;6:20. doi: 10.1186/1471-2288-6-20.
    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. Control Clin Trials. 2002;23:409–21. doi: 10.1016/S0197-2456(02)00208-8.
    1. Montoya L, Liddy C, Hogg W, Papadakis S, Dojeiji L, Russell G, et al. Development of the Champlain primary care cardiovascular disease prevention and management guideline: tailoring evidence to community practice. Can Fam Physician. 2011;57:e202–7.
    1. Donner A. A review of inference procedures for the intraclass correlation coefficient in the one-way random effects model. Int Stat Rev. 1986;54:67–82. doi: 10.2307/1403259.
    1. Ukoumunne OC, Gulliford MC, Chinn S, Sterne J, Burney P. Methods for evaluating area-wide and organisation-based interventions in health and health care: a systematic review. Health Technol Assess. 1999;3(5):iii-92.
    1. Parker DR, Evangelou E, Eaton CB. Intraclass correlation coefficients for cluster randomized trials in primary care: the cholesterol education and research trial (CEART) Contemp Clin 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 controlled trials in primary and residential health care. Aust N Z J Pub Health. 2005;29:461–7. doi: 10.1111/j.1467-842X.2005.tb00227.x.
    1. Yelland LN, Salter AB, Ryan P, Laurence CO. Adjusted intraclass correlation coefficients for binary data: methods and estimates from a cluster-randomized trial in primary care. Clin Trials. 2011;8:48–58. doi: 10.1177/1740774510392256.
    1. Taljaard M, Donner A, Villar J, Wojdyla D, Velazco A, Bataglia V, et al. Intracluster correlation coefficients from the 2005 WHO Global Survey on Maternal and Perinatal Health: implications for implementation research. Paediatr Perinat Epidemiol. 2008;22:117–25. doi: 10.1111/j.1365-3016.2007.00901.x.
    1. Bailey CJ. Metformin: effects on micro and macrovascular complications in type 2 diabetes. Cardiovasc Drugs Ther. 2008;22:215–24. doi: 10.1007/s10557-008-6092-0.
    1. Heran BS, Wong MM, Heran IK, Wright JM. Blood pressure lowering efficacy of angiotensin converting enzyme (ACE) inhibitors for primary hypertension. Cochrane Database Syst Rev. 2009;4CD003823.
    1. Liddy C, Singh J, Hogg W, Dahrouge S, Deri-Armstrong C, Russell G, et al. Quality of cardiovascular disease care in Ontario, Canada: missed opportunities for prevention - a cross sectional study. BMC Cardiovasc Disord. 2012;12:74. doi: 10.1186/1471-2261-12-74.
    1. Shepherd J, Blauw GJ, Murphy MB, Bollen EL, Buckley BM, Cobbe SM, et al. Pravastatin in elderly individuals at risk of vascular disease (PROSPER): a randomised controlled trial. Lancet. 2002;360:1623–30. doi: 10.1016/S0140-6736(02)11600-X.
    1. Zhang C, Rexrode KM, van Dam RM, Li TY, Hu FB. Abdominal obesity and the risk of all-cause, cardiovascular, and cancer mortality: sixteen years of follow-up in US women. Circulation. 2008;117:1658–67. doi: 10.1161/CIRCULATIONAHA.107.739714.
    1. Dunkley AJ, Stone MA, Patel N, Davies MJ, Khunti K. Waist circumference measurement: knowledge, attitudes and barriers in patients and practitioners in a multi-ethnic population. Fam Pract. 2009;26:365–71. doi: 10.1093/fampra/cmp048.
    1. Eldridge SM, Ukoumunne OC, Carlin JB. The intra-cluster correlation coefficient in cluster randomized trials: a review of definitions. Int Stat Rev. 2009;77:378–94. doi: 10.1111/j.1751-5823.2009.00092.x.
    1. Ukoumunne OC. A comparison of confidence interval methods for the intraclass correlation coefficient in cluster randomized trials. Stad Med. 2002;21:3757–74. doi: 10.1002/sim.1330.
    1. Zou G, Donner A. Confidence interval estimation of the intraclass correlation coefficient for binary outcome data. Biometrics. 2004;60:807–11. doi: 10.1111/j.0006-341X.2004.00232.x.

Source: PubMed

Sponsors et collaborateurs

Les conditions médicales

Interventions en matière de drogue

3
S'abonner