13.07.2015 Views

A Simple Poverty Scorecard for the Philippines

A Simple Poverty Scorecard for the Philippines

A Simple Poverty Scorecard for the Philippines

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

To derive a sample-size <strong>for</strong>mula (or equivalently, a <strong>for</strong>mula <strong>for</strong> standard errors),note first that under direct measurement, <strong>the</strong> poverty rate can be estimated as <strong>the</strong>number of households observed to be below <strong>the</strong> poverty line, divided by <strong>the</strong> number ofall observed households. The <strong>for</strong>mula <strong>for</strong> sample size n in this case is (Cochran, 1977):n2z=⎛ ⎞⎜ ⎟ ⋅ pˆ⋅ ( 1 − pˆ), (1)⎝ c ⎠wherez is⎧1.64<strong>for</strong> confidence levels of 90 percent⎪⎨1.96<strong>for</strong> confidence levels of 95 percent⎪⎩2.58 <strong>for</strong> confidence levels of 99 percent,c is <strong>the</strong> confidence interval as a proportion(<strong>for</strong> example, 0.02 <strong>for</strong> an interval of +/–2 percentage points), andpˆ is <strong>the</strong> expected (be<strong>for</strong>e measurement) proportion of householdsbelow <strong>the</strong> poverty line.<strong>Poverty</strong> scorecards, however, do not measure poverty directly, so this <strong>for</strong>mula isnot applicable. To derive a similar sample-size <strong>for</strong>mula <strong>for</strong> <strong>the</strong> Philippine scorecard,consider <strong>the</strong> scorecard applied to <strong>the</strong> validation sample. Figure 2 shows that <strong>the</strong>expected (be<strong>for</strong>e measurement) poverty rate pˆ <strong>for</strong> <strong>the</strong> national line is 31.3 percent (thatis, <strong>the</strong> average poverty rate in <strong>the</strong> construction and calibration sub-samples). In turn, asample size n of 16,384 and a 90-percent confidence level correspond to a confidenceimplies a confidence interval of +/–2.2 percentage points. In fact, USAID has notspecified confidence levels or intervals. Fur<strong>the</strong>rmore, <strong>the</strong> expected poverty rate may notbe 50 percent, and <strong>the</strong> scorecard could be more or less precise than direct measurement.30

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!