The previous post about Dr. Cox, ensnared in a CPT (Child Protection Team) witch hunt in Wisconsin, has led me to evaluate several more research reports on child abuse, including SBS (shaken baby syndrome), AHT (abusive head trauma), and sentinel injuries. These reports are rife with critical assumptions, severe limitations, and gross errors which greatly limit the resulting conclusions in most studies I have reviewed. However, one study that was pointed out to me today takes the cake. I don't know what the prevalence of this degree of misunderstanding is, but CPTs and child abuse pediatricians need make sure they have a proper understanding of sensitivity, specificity, positive and negative predictive value, base rates, etc. And they should not be testifying about the probability of child abuse at all if they don't have this stuff down cold. And I think this means that some proportion of them needs to go back to school or stop testifying.
The article and associated correspondence at issue is entitled The Positive Predictive Value of Rib Fractures as an Indicator of Nonaccidental Trauma in Children published in 2004. The authors looked at a series of rib fractures in children at a single Trauma Center in Colorado during a six year period and identified all patients with a rib fracture. They then restricted their analysis to children less than 3 years of age. There were 316 rib fractures among just 62 children in the series; the average number of rib fractures per child is ~5. The proper unit of analysis for a study looking at positive predictive value is children, sorted into those with and without abuse, and with and without rib fracture(s) as seen in the 2x2 tables below.
The article and associated correspondence at issue is entitled The Positive Predictive Value of Rib Fractures as an Indicator of Nonaccidental Trauma in Children published in 2004. The authors looked at a series of rib fractures in children at a single Trauma Center in Colorado during a six year period and identified all patients with a rib fracture. They then restricted their analysis to children less than 3 years of age. There were 316 rib fractures among just 62 children in the series; the average number of rib fractures per child is ~5. The proper unit of analysis for a study looking at positive predictive value is children, sorted into those with and without abuse, and with and without rib fracture(s) as seen in the 2x2 tables below.
