Monday, March 21, 2011

Car Seats

The American Academy of Pediatrics now advises parents to keep children in rear facing cars seats until age 2.

I am sure that rear facing child seats are somewhat safer at the margins than forward facing car seats.  But, taking a quick look at the study mentioned in the article linked above, makes it clear that that margin is reasonably thin.  First, there's not much difference in the performance of front-facing seats compared to rear-facing seats in frontal crashes, by far the most common type of accident in the data (52% of all crashes).  The biggest difference in child seat performance is side impact crashes, the least common type of accident in the data (16.7% of all crashes).  The study also excludes cases in which child seats exhibited "significant misuse" or where there was no data collected on child seat use (together 31% of the observations). 

Finally, the study is based on---what seems to me---to be an odd compression of the data.  The dependent variables in the analysis is whether a child in an observed accident received a severe injury, defined an an injury receiving an Injury Severity Score (ISI) greater than 9.  I had no idea what an ISI is, but a quick bit of web searching reveals that it is an index ranging from 0 to 75 indicating the total severity of injuries a person has received to various parts of the body.  A person would receive a score of 9 or more if any region of their body has incurred a "serious" injury; he or she would automatically be given a score of 75 if they sustained a lethal injury.  I don't know if the data permit more nuanced analysis, but it seems a bit odd to collapse everything from compound fractures to spinal injuries to fatalities into one big analytic category.  

I remain a bit skeptical about the benefits of child seats and booster seats, especially for older children, and double especially in light of the huge amount of money spent on child seats themselves (and publicity and enforcement of child seats laws) that could be spent on child health and welfare in other ways.  (I am not alone on this point, FWIW.)

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