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Sample Size and Repeated Measures Required in Studies of Foods in the Homes of African-American Families

Citation

Stevens, June; Bryant, Maria; Wang, Chin-Hua; Cai, Jianwen; & Bentley, Margaret E. (2012). Sample Size and Repeated Measures Required in Studies of Foods in the Homes of African-American Families. Journal of Nutrition, 142(6), 1123-1127. PMCID: PMC3349983

Abstract

Measurement of the home food environment is of interest to researchers because it affects food intake and is a feasible target for nutrition interventions. The objective of this study was to provide estimates to aid the calculation of sample size and number of repeated measures needed in studies of nutrients and foods in the home. We inventoried all foods in the homes of 80 African-American first-time mothers and determined 6 nutrient-related attributes. Sixty-three households were measured 3 times, 11 were measured twice, and 6 were measured once, producing 217 inventories collected at ~2-mo intervals. Following log transformations, number of foods, total energy, dietary fiber, and fat required only one measurement per household to achieve a correlation of 0.8 between the observed and true values. For percent energy from fat and energy density, 3 and 2 repeated measurements, respectively, were needed to achieve a correlation of 0.8. A sample size of 252 was needed to detect a difference of 25% of an SD in total energy with one measurement compared with 213 with 3 repeated measurements. Macronutrient characteristics of household foods appeared relatively stable over a 6-mo period and only 1 or 2 repeated measures of households may be sufficient for an efficient study design.

URL

http://dx.doi.org/10.3945/jn.111.150060

Reference Type

Journal Article

Year Published

2012

Journal Title

Journal of Nutrition

Author(s)

Stevens, June
Bryant, Maria
Wang, Chin-Hua
Cai, Jianwen
Bentley, Margaret E.

PMCID

PMC3349983