Objective To examine the representativeness of samples from Shanghai Mass Campaign for Salt Control.
Methods Myer's index (MI), test of goodness for fit, dissimilarity index (DI), and population pyramid were used to examine the distribution of samples versus the total population in Shanghai by various demographic characteristics. The demographic characteristics of subjects in follow-up visits were compared before and after the intervention.
Results This intervention project invited 3 000 households and 7 000 residents in Shanghai, and finally enrolled 2 960 households and 6 886 residents. After unqualified questionnaire sheets were excluded, data from 2 941 households and 6 748 residents were valid and analyzed. The attrition rates of household and individual questionnaires at the 1th, 6th, and 12th months after delivery of salt measuring spoons ranged 0.51%-4.49% and 1.38%-4.70% respectively. No differences were found in the demographic characteristics (such as region, age, gender, education, employment, fixed cook) between the follow-up participants at the 1th, 6th, and 12th months and baseline subjects (all P>0.05). The MI was 7.47 for the total sampled population, 8.70 for the male, and 6.35 for the female, all less than 10. The population pyramid diagrams (total, male, and female)showed a symmetrical distributions of various age groups of the sampled population and the total population of Shanghai in 2008. Using the 2008 Shanghai population data as reference for test of goodness for fit, the chi-square values for total, male, and female sampling population were 5.30, 5.88, and 4.84, respectively (all P>0.05). In addition, the DIs were 10.34, 10.72, and 9.96, respectively.
Conclusion The intervention project is featured by low attrition rates and no demographic differences between participants in follow-up visits and at baseline, indicating high consistency. Fair age distributions between the sampled population and the total Shanghai population indicate a good representativeness of the sampling subjects. It is therefore valid to conclude that the intervention results can be extrapolated to the general Shanghai population.
DownLoad: