Samples came from six major metropolitan areas: San Francisco, Boston, Minneapolis, Los Angeles, New York City, and Seattle. That is essentially most of America's workforce. A study published on Tuesday in PLoS Medicine suggests that boosting vitamin D levels with supplements would not help. Pool testing allows scientists to test samples more efficiently, analyzing many samples at once. To test samples more efficiently, the researchers used a technique called 'pooling.'
Six countries are listed in the study.
( z0 list :ARG1 ( z1 country :quant 6 ) :ARG2 ( z2 study ) )
(z0 / list-01
    :ARG1 (z1 / country
              :quant 6)
    :ARG2 (z2 / study-01))
Six countries are listed in the study .
z1 :quant 0
z0 :ARG1 z1
z0 :ARG2 z2