Complex sentence: During the first year, this anti-fraud change resulted in seven million fewer dependents being claimed, nearly all of which are believed to have involved either children that never existed, or tax deductions improperly claimed by non-custodial parents.
Split into simpler sentences: During the first year, this anti-fraud change resulted in seven million fewer dependents being claimed. It is believed the disappearing dependents were either children that never existed, or tax deductions improperly claimed by non-custodial parents.