component of domestic absorption in the national accounts.<sup>6</sup> There has been a systematic gap between mean consumption or income measured from the household surveys used to measure poverty and these national accounts aggregates, and there has also been a gap in the growth rates, such that the share of GDP accountable to consumption by households has tended to fall in many developing countries (Ravallion, 2003; Deaton, 2005). The way national accounts are constructed in practice means that there is nothing exactly corresponding to household consumption as measured in surveys, so the comparison is difficult. Differences in the concepts play a role, but so too do measurement errors (in both sources), differences in accounting periods and sampling problems. (It should not be assumed that national accounts data are more accurate than survey data for developing countries.) To investigate this further, I have assembled a data file of the longest available spells between two household surveys for developing countries, using the same welfare indicator (consumption or income) for both surveys. This was possible for 95 developing countries, with a mean (and median) of 16 years between the surveys, ranging from 4 to 32 years. Regressing the annualized growth rate in the survey means on the corresponding growth rate in the survey mean the slope coefficient is 0.968 (White s.e.=0.199; n=95) and the intercept is -0.012 (s.e.=0.006). Figure 1 plots the data points. Imposing the restriction that the slope is unity, the average gap is - 0.012 (s.e.=0.004), indicating that the survey means give a 1.2 percentage point lower growth rate on average.<sup>7</sup> This is significantly different from zero, but there is still a wide variation (Figure 1), with a standard deviation of 4.0 percentage points, and a range from -20.7 to 8.1 points. Some of this is clearly due to measurement errors in both the surveys and national accounts. On top of the errors in both data sources, there are errors in matching survey periods to national accounting periods. Dropping just three (large-negative) outliers that may well reflect measurement errors in the surveys, the mean gap between growth rates falls to 0.7 points (s.e.=0.3).<sup>8</sup>

> 6 For the poverty measures reported here, two-thirds of the surveys used consumption, which is taken to be the preferred welfare metric. When consumption is not available, income is used instead.

> 7 These are simple un-weighted means across countries, for descriptive purposes. The poverty forecasts based on the World Bank’s current growth rate projections reported later were built up from the country level and are implicitly) weighted. These incorporate country specific adjustment factors for gaps

> 8 India has been prominent in recent discussions of the gap between survey data aggregates and national accounts aggregates (Ravallion, 2003; Deaton, 2005). Over the longest available spell between surveys for India (1977/78 to 2009/10) the annual growth rate in mean consumption from the surveys has been 1.4%, as compared to 2.0% from the private consumption component of the national accounts. This gap is in line with the average. But it is a sizable gap over such a long period.

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