Statistical analysis
Data was entered into Microsoft Excel (Microsoft, WA) and statistics
were computed within the software. Binomial Exact tests and Wilson’s
Confidence Intervals were used to determine if the cohort’s
seropositivity was significantly different than the general population’s
rate. The general population’s seropositivity rates were chosen from
long-term studies of antibody persistence. Seropositivity for measles,
mumps, and rubella were set at 95%, 74%, and 100% respectively as
found by Davidkin et. al, 15-20 years after
vaccination.14 Rubella seropositivity was adjusted to
99% to avoid divide by zero errors within Excel. Varicella
seropositivity was set to 99% based on the results of Vessey et al. and
Watson et al. 15,16who took titers at one and six
years respectively. Although Vessey et al. found 100% seropositivity at
one year, a rate of 99% eliminates divide by zero errors in Excel.
Tetanus seropositivity was set at 85.8% as found by Borella-Venturini
et al.17 for those who received <5 doses.
Not all subjects received the 4th and
5th doses of the DTaP vaccine and therefore this value
represents a more accurate representation of the cohort. Hepatitis B had
a greater literature base from which to choose a seropositivity rate. In
following the CDC citations, seropositivity was set at 66% (15-year
mark) as reported by McMahon et al.18