Steven Levitt may be trying to show that car seats are not really useful for children above age two but after a very brief research into this topic I was surprised to discover some facts and reports. Among them one especially stood out:

An Accident Study of the Performance of Restraints Used by Children Aged Three Years and Under – A study commissioned by ANEC, the European consumer voice in standardisation, AISBL” [PDF]

Nine month old child and same child at three and a half years old in same large Nordic rearward facing child seat installed in a VW Golf

Nine month old child and same child at three and a half years old in same large Nordic rearward facing child seat installed in a VW Golf

Any parent who carries his or her child in an automobile should read this important report. It includes lots of data but its introduction and conclusion are just a few pages. Pages that can dramatically affect your choice for a child car seat and the safety of your child: More