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A Simple Poverty Scorecard for the Philippines

A Simple Poverty Scorecard for the Philippines

A Simple Poverty Scorecard for the Philippines

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The 90-percent confidence interval <strong>for</strong> <strong>the</strong> differences <strong>for</strong> scores of 20–24 is +/–2.4 percentage points (Figure 7). 19 This means that in 900 of 1,000 bootstraps, <strong>the</strong>difference between <strong>the</strong> estimate and <strong>the</strong> true value is between –1.0 and 3.8 percentagepoints (because 1.4 – 2.4 = –1.0, and 1.4 + 2.4 = 3.8). In 950 of 1,000 bootstraps (95percent), <strong>the</strong> difference is 1.4 +/–2.8 percentage points, and in 990 of 1,000 bootstraps(99 percent), <strong>the</strong> difference is 1.4 +/–3.5 percentage points.For almost all score ranges, Figure 7 shows differences—sometimes large ones—between estimated poverty likelihoods and true values. This is because <strong>the</strong> validationsub-sample is a single sample that—thanks to sampling variation—differs indistribution from <strong>the</strong> construction/calibration sub-samples and from <strong>the</strong> <strong>Philippines</strong>’population. For targeting, however, what matters is less <strong>the</strong> difference in all scoreranges and more <strong>the</strong> difference in score ranges just above and below <strong>the</strong> targeting cutoff.This mitigates <strong>the</strong> effects of bias and sampling variation on targeting (Friedman,1997). Section 9 below looks at targeting accuracy in detail.Of course, if estimates of groups’ poverty rates are to be usefully accurate, <strong>the</strong>nerrors <strong>for</strong> individual households must largely cancel out. This is generally <strong>the</strong> case, asdiscussed in <strong>the</strong> next section.Ano<strong>the</strong>r possible source of bias is overfitting. By construction, <strong>the</strong> scorecard hereis unbiased, but it may still be overfit when applied after July 2004 (<strong>the</strong> end date of <strong>the</strong>2004 APIS). That is, it may fit <strong>the</strong> 2004 APIS data so closely that it captures not only19Confidence intervals are a standard, widely understood measure of precision.26

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