Ma et al. BMC Public Health 2012, 12:568 http://www.biomedcentral.com/1471-2458/12/568 consumed on ≧4 days. These scores were summed to give a possible range of 0-16, and then new scores were assigned as described in Table 1 to reflect age-specific distribution. The final CS-ICFI was a summation of the scores obtained for each variable described above. The index ranged from 0 to 10 for all three age groups. The CS-ICFI was divided into 3 categories based as closely as possible on tertiles with all age groups to- gether in the following manner: a score of 0-7 was con- sidered low, 8 was considered medium, and 9-10 was considered high. Another index was constructed to summarize the in- formation from the 3 CS-ICFIs corresponding to the 3 visits. Each CS-ICFI was coded 0 for low, 1 for medium, and 2 for high. These scores were summed over the 3 vis- its for each infant to give a possible range of 0-6. The so- called continuous L-ICFI was then cut based on tertiles in the following manner: 0-2 was considered low, 3 was considered medium, and 4-6 was considered high [9]. Statistical analysis The associations between the CS-ICFIs or L-ICFI with LAZ, WAZ and WLZ were analysed using anthropomet- ric data from visit 3. Linear regression models was used to analyze the association of each component of the CS- ICFIs with LAZ, WAZ and WLZ at Visit 3, and the asso- ciation of L-ICFI with LAZ, WAZ and WLZ at Visit 3. For each model, birth weight, mother’s pre-pregnancy height and weight, and annual household income were adjusted as confounders. The association between CS- ICFIs and LAZ, WAZ and WLZ at Visit 3 was also examined by a linear regression model, and child sex and age, birth weight, mother’s pre-pregnancy height and annual household income were adjusted as confounders. Changes in the distribution of CS-ICFI components over time were examined at the group level. Chi-square test was used to explore whether the distribution of the CS-ICFI components differed between different visits. To examine the longitudinal changes of CS-ICFI and eventually obtain L-ICFI value for each infant we had to take into account a disturbing factor: that the CS-ICFI scoring system does change across age categories. There- fore, first, to make CS-ICFI values comparable over time we decided to normalize their distribution and to use the z scores instead of original CS-ICFI values. Second, we were challenged by the choice of a statistical model to test whether these CS-ICFI z values were stable for each infant from one visit to the other. To estimate the stability of 3 visits, we used repeatability coefficient (RC) which was also referred to as interclass correlation coef- ficient proposed by Moursi [9]. RC [13] is the ratio of the between-subject variance divided by the sum of the between-subject and the within-subject variance applied Page 4 of 9 to test the repeatability of measures from the same sub- ject. The variance for the 3 visits’ CS-ICFI z values of the same infant was considered conceptually an equiva- lent of the within-subject part of the total variance of the measurement which is recommended to estimate the measurement error [14]. Because we used normalized values (z scores), the total variance of all the CS-ICFI z values was 1. RC ranges between 0 and 1, with RC = 0 indicating no repeatability at all (absence of stability from visit to visit) and RC = 1 indicating perfect repeat- ability (perfect stability from visit to visit). Thus, it is possible to test whether the RC is significantly different from zero. All analyses were performed by using SPSS 13.0 for windows and statistical significance was set at 0.05. Results Loss to follow-up There were no significant differences in mean LAZ (P = 0.217), mean WAZ (P = 0.346), mean WLZ (P = 0.689), mean age (P = 0.062), and sex ratio (P = 0.457) of the 29 infants whose caregivers did not complete the question- naires versus the infants with complete data set at Visit 2. Similarly, the 68 infants who had uncompleted question- naires at Visit 3 did not differ significantly from the remaining sample with respect to mean LAZ (P = 0.779), mean WAZ (P = 0.510), mean WLZ (P = 0.453), mean age (P = 0.217), and sex ratio (P = 0.091) at Visit 3. Sample characteristics Main sample characteristics of 3 visits are shown in Table 2. The mean ages of these 180 infants at 3 visits were (5.85 ± 0.44), (12.13 ± 0.29), and (18.12 ± 0.27) months, respectively. Among them, there were 79 boys (43.89%) and 101 girls (56.11%). Most children grew well in this community. Evaluated by the WHO Child Growth Standards, child mean LAZ, WAZ and WLZ of 3 visits were all above the WHO median. There were only one infant (0.38%) stunting (LAZ < -2) at Visits 2 and 3, and another one (0.38%) wasting (WLZ < -2) at Visit 3. There was no underweight (WAZ < -2) infants over the study period. However, the rates of overweight (WLZ > +2) of infants at 3 visits were 6.11%, 5.00% and 5.00%, respectively. Breastfeeding was relatively common during the first 6 months but did not last into the second year of life; 48.89% of infants in our sample were breastfed at base- line, but at Visit 3, only 1.67% was breastfed. Distribution of the CS-ICFI components at different time points Many of the components of the CS-ICFI varied with time at the group level (Table 3). As expected, breastfeeding decreased over time as infants grew. At the same time,