The analysis of consistency between reported and directly measured values in 2008-2009 were based on the premise that, in all of the comparisons, the values presented represent a mean estimate of the Brazilian population in the state capitals and metropolitan areas.
The height and weight means were stratified year on year from 20 to 29 years old and biennia between 30 and 39 years old to maintain the homogeneity of the sample.
The VIGITEL and POF height and weight means were compared statistically for each age with values effectively measured using the student’s t-test. The p values
To show the effect of the reported and directly measured measurements, the values for height, weight and Body Mass Index were log-transformed and the differences versus the means plotted, as proposed by Bland & Altman. 2
Differences in values for height between POF and VIGITEL presented no systematic characteristics in men and were not associated with age. Differences in values for weight were not associated with age and the difference between means was not statistically significant at any age. There was no link between the differences in mean weight and the differences in mean height, i.e., when mean weight was higher in VIGITEL, mean height did not follow any trend of being higher or lower (Table 1).
Ten of the 15 difference in height values were statistically significant for women. The mean height in VIGITEL was higher than that in POF in eight cases. In ten comparisons, VIGITEL values exceeded those of POF for weight and in all of the comparisons of over 30s. The values for height were higher in VIGITEL in almost all of the comparisons. The VIGITEL values exceeded mean values in the POF in the majority of comparisons of weight values (Table 1).
Stratification of the comparisons by age shows, however, fewer similarities between the two surveys, especially in the classification of women as underweight or obese.
The VIGITEL values were higher than those estimated in the POF for the same age groups in men. In women, the expression of higher values in the obesity estimates varied between 20 and 29 years old and tended to be higher in VIGITEL from this age and upwards (Figure 1).
The dispersion of differences proportional to the mean between the two surveys was greater among females than males, notably for weight values. For women, the height and weight values in VIGITEL exceeded those observed in the POF by an average of around 5%. For males, the trend for VIGITEL values to exceed POF values still existed, although in magnitudes the proportional differences of which were close to zero (Figure 2).
Comparison between reported and directly measured height and weight values in the Brazilian population of the state capitals and the Federal District in 2008-2009 shows: a) height and weight values reported by the interviewee tend to be higher than those directly measured in the same population; b) men are less imprecise and inexact than women when providing anthropometric data; c) overall estimates based on BMI calculated using reported or measured values are relatively close; d) there is greater variability in obesity estimates when stratified by age; e) the differences between measured and reported values are more pertinent to females. By restricting the age range in the study, this analysis avoided the results being influenced by anthropometric fluctuations typical of growth completion in adolescence and of ageing.