Complex sentence: This increase in efficiency can offset the advantages offered by free-response items; if free-response items provide twice as much information but take four times as long to complete, the multiple-choice items present a better measurement tool.
Split into simpler sentences: This increase in efficiency can offset the advantages offered by free-response items. That is, if free-response items provide twice as much information but take four times as long to complete, multiple-choice items present a better measurement tool.