(the most recent poverty report isn't currently downloadable due to the recent government shutdown)
Your question about why the official poverty measure is still used at all is a good one. I'd speculate that if the official poverty measure is tangled up with legislation, it may not be simple for government bureaus to update the measure and eliminate usage of the old measure without someone passing some new laws. If the poverty measure partly defines who does or doesn't receive certain benefits then changing it could be fairly political. If the supplemental poverty measure indicates that e.g. 12% not 10% of families fall below the poverty line, then that implies 20% more funding is necessary for some benefits.
(the most recent poverty report isn't currently downloadable due to the recent government shutdown)
Your question about why the official poverty measure is still used at all is a good one. I'd speculate that if the official poverty measure is tangled up with legislation, it may not be simple for government bureaus to update the measure and eliminate usage of the old measure without someone passing some new laws. If the poverty measure partly defines who does or doesn't receive certain benefits then changing it could be fairly political. If the supplemental poverty measure indicates that e.g. 12% not 10% of families fall below the poverty line, then that implies 20% more funding is necessary for some benefits.