BMC Public Health 2004, 4 http://www.biomedcentral.com/1471-2458/4/22 sion was also used to estimate the association between consumption of green vegetables and salads, as depend- ent variable, and item responses. This variable was selected because food insecurity was associated with reduced consumption of green vegetables and salads. Regression analyses were adjusted for continuous variable age, sex and ethnic group. We also tested whether associ- ations differed according to ethnic group. Robust standard errors were estimated to allow for clustering by household [20]. Results There were 631 eligible adults and food security data were obtained for 531 (84%) subjects from 286 households. There were 134 (25%) of subjects who were classified as food insecure, based on a definition of two affirmative items out of six. Table 1 lists the six items of the house- hold food security scale in rank order of frequency of affirmative responses, with the exception that item number eight is listed after item number five with which it is associated. Items are numbered following Blumberg et al [4]. Item-score correlations ranged between 0.52 to 0.79. The value of Cronbach's alpha, an index of internal consistency, was 0.87. In the Afro-Trinidadian ethnic group, Cronbach's alpha was 0.84, in Indo-Trinidadians 0.90 and in the mixed group 0.83. Table 1 also gives esti- mated threshold values from the Rasch model for each of the items. It was clear that the 'balanced meal' item gave the lowest severity threshold in this dataset. The severity rankings of the other items were consistent with US data. Table 2 shows the frequency of discordant responses for individuals from the same household, by household size, and the intraclass correlation coefficient. The latter is equivalent to the kappa statistic where households are considered as observations and individual subjects as raters. The overall proportion of discordant responses was low and the ICC was high for each item and for the food insecurity classification. Table 2: Responses obtained from households with more than one respondent, and intraclass correlation coefficient. Figures are frequencies (column percent) except where indicated. Discordant responses by household size ICC (95% CI) Two respondents (120) Three respondents (30) Four respondents (15) Table 3: Item responses and correlations by ethnic group. Figures are frequencies (column percent) except where indicated. Afro-Trinidadian Indo-Trinidadian Mixed Affirmative (%) Item-score correlation Affirmative (%) Item-score correlation Affirmative (%) Item-score correlation 3 2 5 8 7 10 3 2 5 8 7 10 Item 'Balanced meal' 'Food last' 'Skip meals' 'How often' 'Eat less' 'Hungry' Food insecurity 155 'Balanced meal' 65 (42) 'Food last' 54 (35) 'Skip meals' 49 (32) 'How often' 36 (23) 'Eat less' 44 (28) 'Hungry' 15 (10) 9 (8) 9 (8) 9 (8) 8 (7) 5 (4) 2 (2) 11 (9) 0.54 0.71 0.74 0.49 0.76 0.51 7 (23) 4 (13) 4 (13) 4 (13) 3 (10) 2 (7) 7 (23) 1 (7) 3 (20) 3 (20) 2 (13) 1 (7) 1 (7) 4 (27) 0.78 (0.73 to 0.83) 0.73 (0.67 to 0.79) 0.70 (0.63 to 0.76) 0.71 (0.65 to 0.77) 0.78 (0.73 to 0.83) 0.77 (0.72 to 0.82) 0.68 (0.61 to 0.75) 246 48 (20) 26 (11) 23 (9) 21 (9) 19 (8) 9 (4) 0.61 0.77 0.80 0.79 0.85 0.58 106 42 (40) 26 (25) 21 (20) 13 (12) 11 (10) 6 (6) 0.49 0.66 0.72 0.53 0.74 0.43 Page 4 of 9 (page number not for citation purposes)