**Table 3: Population by age groups and extreme poverty**

|**GMD Sample of develop**|**Extreme poor**<br>**(millions)**<br>**ing countries**|**Headcount**<br>**poverty rate**|**Share of**<br>**extreme poor**<br>**(%)**|**Share of**<br>**population**<br>**(%)**|
|---|---|---|---|---|
|Children0-17|328.7|19.5|50.2|32.1|
|_Children 0-4 _|_104.0_|_21.0_|_15.9_|_9.4_|
|_Children 5-9 _|_101.1_|_21.5_|_15.4_|_9.0_|
|_Children 10-14_|_84.4_|_18.7_|_12.9_|_8.6_|
|_Children 15-17_|_39.1_|_14.6_|_6.0_|_5.1_|
|Adults (18 or more)|326.3|9.2|49.8|67.9|
|_Adults 18-59_|_288.1_|_9.5_|_44.0_|_57.6_|
|_Adults 60 or more_|_38.2_|_7.0_|_5.8_|_10.3_|
|Total|655.0|12.5|_100.0_|_100.0_|

Source: GMD, UNDESA, WDI, PovcalNet While these differences in poverty rates by age group are large, how precisely are they estimated? The sample consists of a roughly 7.7 million observations on individuals, randomly selected under each survey’s design from a population of about 5.3 billion people living in the 89 countries included in the sample. Estimating proper standard errors, however, is complicated by the absence of identifiers for the primary sampling units for many of the surveys in the GMD. Without these identifiers, it is impossible to properly adjust for survey design when calculating standard errors and to give confidence intervals for the full sample. Therefore, Table 4 reports confidence intervals around average poverty estimates by age group, for the 49 countries for which the primary sampling units (PSU) can be identified. Average poverty rates are significantly higher in this subsample. The size of the confidence interval tends to be modest, however, ranging from 1 to 1.5 percentage points. A back of the envelope estimate is that the use of this subsample of 49 countries, instead of the full sample of 89, inflates the estimated size of the confidence interval by 1.42.10 This implies that the corresponding confidence intervals for the full sample would range from approximately 0.5 to 1 percentage point. With the exception of the small difference in poverty rates between the two youngest age groups, we therefore conclude that the declines in aggregate estimated poverty rates by age group reported in Table 3 are all statistically significant.

The welfare disadvantage faced by children, relative to adults, is also reflected in Figures 1 and 2, which give the cumulative and probability density functions of welfare by age group. Figure 1 indicates that the distribution for adults stochastically dominates that of children, meaning that poverty rates for children are higher at any poverty line. Furthermore, although the differences are smaller, children 10-17 are slightly better off than younger children throughout most of the distribution. Finally, Figure 2 demonstrates the fat left tail of the child welfare distribution, and the large mass of children that live on slightly less than the $3.10 per day moderate poverty line.

10 1.42 is approximately equal to the square root of the ratio of the number of observations in the full sample (7.7 million) to the number of observations in the subsample used in Table 9 (3.8 million). The square root of the ratio of 89 countries in the full sample to 49 in the subsample is 1.35. This estimate assumes that the samples in the 49 countries with PSI identifiers are on average as precise as the 40 that are missing this information. In addition, it slightly overstates the size of the confidence interval by failing to account for the slight gain in precision that would arise due to the lower estimated poverty rate in the full sample.

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