BACKGROUND: Cluster designs have become increasingly popular in many research areas. Adopting these designs requires special considerations because individuals within the same cluster may be correlated. Therefore, appropriate sample size calculations in these settings require the incorporation of additional information regarding intraclass or intracluster correlations (ICCs), which measure the degree of similarity between individuals within the same cluster or class. OBJECTIVES: To discuss the importance of the ICC in cluster-designed studies and present ICC estimates for selected physiologic characteristics in children and adolescents. METHOD: The ICCs for body mass index (BMI), sum of skinfolds (SSF), blood pressure, glucose, insulin, and lipids were determined using baseline data from the Cardiovascular Health in Children and Youth Studies (CHIC II and III). The ICC estimates presented were obtained through the use of mixed models for the entire data set and separately by age groups, gender, and ethnicity. RESULTS: The estimated ICCs ranged from .0104 for BMI to .1657 for glucose. The differences in the estimated ICCs among the three age groups were most marked for blood pressure, SSF, and glucose and were small for aerobic power, insulin, and lipids. The greatest difference in ICC by gender was in BMI and SSF: The ICC for SSF in girls was 8.2 times larger than that for boys. Caucasians had higher ICC estimates for insulin than did African Americans and other ethnic groups. DISCUSSION: The magnitude of the ICC varied by the outcome of interest, and factors such as age, gender, and ethnicity also influenced the magnitude of the ICC. The presence of ICCs should be assumed when using cluster designs, and ICCs should be considered when conducting sample size calculations for such studies.
BACKGROUND: Cluster designs have become increasingly popular in many research areas. Adopting these designs requires special considerations because individuals within the same cluster may be correlated. Therefore, appropriate sample size calculations in these settings require the incorporation of additional information regarding intraclass or intracluster correlations (ICCs), which measure the degree of similarity between individuals within the same cluster or class. OBJECTIVES: To discuss the importance of the ICC in cluster-designed studies and present ICC estimates for selected physiologic characteristics in children and adolescents. METHOD: The ICCs for body mass index (BMI), sum of skinfolds (SSF), blood pressure, glucose, insulin, and lipids were determined using baseline data from the Cardiovascular Health in Children and Youth Studies (CHIC II and III). The ICC estimates presented were obtained through the use of mixed models for the entire data set and separately by age groups, gender, and ethnicity. RESULTS: The estimated ICCs ranged from .0104 for BMI to .1657 for glucose. The differences in the estimated ICCs among the three age groups were most marked for blood pressure, SSF, and glucose and were small for aerobic power, insulin, and lipids. The greatest difference in ICC by gender was in BMI and SSF: The ICC for SSF in girls was 8.2 times larger than that for boys. Caucasians had higher ICC estimates for insulin than did African Americans and other ethnic groups. DISCUSSION: The magnitude of the ICC varied by the outcome of interest, and factors such as age, gender, and ethnicity also influenced the magnitude of the ICC. The presence of ICCs should be assumed when using cluster designs, and ICCs should be considered when conducting sample size calculations for such studies.
Authors: S R B Verjans-Janssen; Dave H H Van Kann; Sanne M P L Gerards; Steven B Vos; Maria W J Jansen; Stef P J Kremers Journal: BMC Public Health Date: 2018-07-06 Impact factor: 3.295
Authors: David R Lubans; Philip J Morgan; Deborah Dewar; Clare E Collins; Ronald C Plotnikoff; Anthony D Okely; Marijka J Batterham; Tara Finn; Robin Callister Journal: BMC Public Health Date: 2010-10-28 Impact factor: 3.295
Authors: Carlos Antônio S T Santos; Rosemeire L Fiaccone; Nelson F Oliveira; Sérgio Cunha; Maurício L Barreto; Maria Beatriz B do Carmo; Ana-Lucia Moncayo; Laura C Rodrigues; Philip J Cooper; Leila D Amorim Journal: BMC Med Res Methodol Date: 2008-12-16 Impact factor: 4.615
Authors: Wilma Jansen; Hein Raat; Evelien Joosten-van Zwanenburg; Ivo Reuvers; Ron van Walsem; Johannes Brug Journal: BMC Public Health Date: 2008-07-25 Impact factor: 3.295
Authors: M Willeboordse; M W Jansen; S N van den Heijkant; A Simons; B Winkens; R H M de Groot; N Bartelink; S P Kremers; P van Assema; H H Savelberg; E de Neubourg; L Borghans; T Schils; K M Coppens; R Dietvorst; R Ten Hoopen; F Coomans; S Klosse; M H J Conjaerts; M Oosterhoff; M A Joore; I Ferreira; P Muris; H Bosma; H L Toppenberg; C P van Schayck Journal: BMC Public Health Date: 2016-07-26 Impact factor: 3.295