Original data reference: O'Brien, K. L., L. H. Moulton, R. Reid, R. Weatherholt, J. Oski, L. B. Brown, G. Kumar, A. Parkinson, D. Hu, J. Hackell, I. Chang, R. Kohberger, G. Siber, and M. Santosham. 2003. Efficacy and safety of seven-valent conjugate pneumococcal vaccine in American Indian children: Group randomised trial. Lancet 362: 355-361. https://doi.org/10.1016/S0140-6736(03)14022-6.
Hayes, R. J., and L. H. Moulton. 2009. Cluster Randomised Trials. Boca Raton, FL: CRC Press.