Data were collected during the baseline measurements for the Pacific Obesity Prevention In Communities (OPIC) study: a muti-site intervention aiming to reduce overweight/obesity among predominately Pacific adolescents. Data for the current study were collected at the New Zealand site; study participants were drawn from seven high schools in a geographically defined, economically disadvantaged area during the 2005 school year. All seven schools were deciles one or two. School deciles reflect the socioeconomic position of the attending students and range from one to 10; decile-one represents most deprived while decile-ten represents the least deprived. One school of the original seven was excluded from this analysis due to poor student response rate (25%).
All students attending the school during the days of data collection were invited to participate. From the remaining six schools, 3245 students agreed to participate (response rate 62%). Final analyses were conducted with the 3119 students who had complete survey data about nutrition and physical activity patterns and physical measurements. Parents of students under age 16 and students aged 16 years and older consented to participation. The University of Auckland Human Participants Ethics Committee granted ethical approval for the study.
Height and weight measurements were taken by trained research staff using standardized protocols. Students wore light clothing and no shoes. Students' weights were measured to the nearest 0.1 kilogram using a digital scale. Students' heights were measured to the nearest 0.1 centimeter using a free-standing portable stadiometer. Body mass index (BMI) was calculated as weight (kilograms) divided by height (meters) squared.
All remaining measures were assessed by self-report using a handheld computer. The survey items were pilot tested for comprehension with four school classes, one class at each school level. Frequency of family meals was assessed with the question, "In the last 5 school days, how many times did all or most of your family living in your house eat an evening meal together?" Response options ranged from 0 to 5 days and were collapsed into "none," "1 to 2 days," "3 to 4 days," and "everyday" for analysis.
Mother/father support for healthy eating were assessed with two questions asking how much does your mother (or female caregiver)/father (or male caregiver) encourage you to eat healthy foods. Students could respond "a lot," "some," "a little," or "not at all." For analysis, response options for mother/father support for healthy eating were dichotomized into "a lot" or "some, a little, or not at all. "Parental limits on television use was assessed by asking students if their parents limited the amount of TV, videos and DVDs they were allowed to watch during the school week. Response options included "no limits," "yes, but not very strict limits," or "yes, strict limits." Response options were dichotomized for analysis into "yes, strict limits or yes, but not very strict limits" or "no." Home availability of fruit, chips, chocolates, and soft drinks were assessed by four separate questions each with the responses "everyday," "most days," "some days," or "hardly ever". Home availability of fruit was dichotomized at "everyday" and "most days, some days, or hardly ever." Home availability of chips, chocolates and soft drinks were dichotomized at "everyday or most days" or "some days or hardly ever."
Students were asked about their frequency breakfast consumption and soft drink consumption over the last five school days. These two items were measured in relation to the previous five school days because they were directly relevant to key intervention strategies of the study. For all other nutrition behaviours students were asked to report their usual consumption. It is generally easier for subjects to describe their usual consumption of foods, rather than what was eaten at a specific time in the past . This concept refers to generic memory (rather than episodic) and has been frequently used by epidemiologists investigating food-borne illnesses . Two separate items assessed usual daily fruit and vegetable consumption. Responses were summed and dichotomized to reflect national recommendations for fruit and vegetable consumption (5 or more per day) . Bringing lunch from home was assessed with one question asking where students usually got their lunch from. Students could choose from home, school canteen, shops (takeaway food outlet or convenience stores), friends, or that they did not eat lunch. Options were dichotomized into "home" or "school, shops, friends or no lunch" for analysis. Usual fast food/takeaway food consumption was assessed with a single question with five response options ranging "most days" to "once a month or less." Responses were dichotomized at once a week or more. Frequency of eating fried food, chocolates, sweets or ice cream, and fruit as after school snacks were assessed with four separate items. Responses included "everyday or almost everyday," "most days," "some days," and "hardly ever or never" and were dichotomised at "most or some days." Student's ethnicity, age and gender were each assessed by self-report.