What is the lowest child sex ratio in groups where employment is 31.3%?
CREATE TABLE "statistics" (
  "religious_group" text,
  "population_pct" text,
  "growth_1991_2001" text,
  "sex_ratio_total" real,
  "literacy_pct" text,
  "work_participation_pct" text,
  "sex_ratio_rural" real,
  "sex_ratio_urban" real,
  "sex_ratio_child" real
);
SELECT MIN("sex_ratio_child") FROM "statistics" WHERE "work_participation_pct"='31.3%';