Ma et al. BMC Public Health 2012, 12:568 http://www.biomedcentral.com/1471-2458/12/568 mean WAZ and WLZ, respectively. Though food consistency taking the place of bottle feeding is an in- novative attempt, however, it raises some questions. First, the majority of young children aged 18 months re- ceiving solid staple food resulted in small sample size in the low food consistency group which might affect the accuracy of the statistical results. Second, high food consistency generally accompanied with high energy density may offer more energy intakes [16]. Food consistency used as a component of CS-ICFI may drive the relationship of L-ICFI with WAZ. Therefore, food consistency score should be used with caution and needs to be investigated in future studies. It has been pointed out that a 24-h recall cannot ap- propriately reveal the actual quality of the diet, mainly because of possible variations from one day to another [3]. In our context, due to some special Chinese diet habits, food groups varied not much within 24 h, so it was better to count number of food groups consumed based on the information collected from the past 7 days. Therefore, we tested a slightly modified version of diet- ary diversity based on 7-d recalls, which actually has been applied in two recent studies [8,17]. Several stud- ies have illustrated that food diversity was a good indi- cator of adequate micronutrient intake and associated with child nutritional status [18-20]. Our findings also confirmed that both dietary diversity and food group frequency score were associated with LAZ among 18- month-old infants. Furthermore, it is suggested that both dietary diversity and food group frequency score are likely driving the relationship of L-ICFI with LAZ. Challenges in constructing a longitudinal ICFI The first consideration in constructing a longitudinal ICFI is the stability of CS-ICFIs over the study period at the individual level. To test the stability, we applied repeatability coefficient proposed by Moursi [9], which was also referred to as interclass correlation coefficient and used to test the re- producibility of replicate measures from the same sub- ject, with 0 indicating no stability over time at all and 1 indicating perfect stability from visit to visit. Fortunately, we found that the value of repeatability coefficient was 0.14 which differed significantly from zero. This value means that the CS-ICFI is relatively stable over time at least at the individual level and it is feasible to construct L-ICFI using the information from several CS-ICFIs. Furthermore, changes in the distribution of the CS- ICFI components by different age groups were determin- ant for the relative stability of CS-ICFI. As expected, infants were breastfed less as they grew older, whereas feeding frequency, food consistency and food diversity all increased over time. In addition, due to the obvious decrease of breastfeeding as infants grew in our context, Page 8 of 9 we had to modify the scoring methods of food group fre- quency and feeding frequency for elder infants which were not divided into tertiles to harmonize the whole scoring system of CS-ICFI. As a result, the decline of the CS-ICFI as breastfeeding dropped with age partly compensated for by higher feeding frequency, food consistency and food diversity led to the slight increase of CS-ICFI scores over time. Therefore, we acknowl- edged that the stability might not be very strong as Moursi reported in their study even if the RC was statis- tically significantly different from zero. Despite the variations in the methods used to build CS-ICFI, and the limitation in the construction of L-ICFI, our results confirmed the existing litera- ture and suggested that ICFI was positively asso- ciated with anthropometric indicators of nutritional status among infants and young children [2,3,9]. In addition, our study has a noteworthy finding. This is the first attempt to apply ICFI in an affluent down- town area in China different from the previous studies conducted in relatively impoverished settings. The rate of overweight of infants was higher in the surveyed area. The CS-ICFI at 6 months positively associated with not only child LAZ but also WAZ and WLZ at 18 months may be due to the affluent setting with high rate of over- weight in infants, which was similar to the results in a study conducted in China’s rural areas[6]. However, there was no association between longitudinal ICFI and WLZ in our study suggested that ICFI was related with optimal nutritional status of infants and young children in the long term and might be used in more affluent areas in further studies. Our study also has several limitations. First, the data were only collected from a community in Shanghai which could not represent the general conditions of child feeding practice in China. Secondly, because the caregivers reported about themselves with no objective reporters, the risk of reporting bias may exist. Addition- ally, there may be some unmeasured confounders which probably had some influence on the results. Conclusion In conclusion, CS-ICFI at 6 months was positively asso- ciated with child growth status at 18 months indicated that previous feeding practice may predict future growth of children. Moreover, the longitudinal ICFI which was constructed with use of data collected from a brief recall based on cross-sectional studies was positively associated with LAZ and WAZ. It is suggested that ICFI can be used to evaluate the effects of child feeding practice on child growth for a longer time. Competing interests The authors declare that they have no competing interests.