A Statistical Confidence Interval for True Per Cent Reduction in Caries-Incidence Studies

¹ Division of Dental Research, The Procter & Gamble Company, Cincinnati, Ohio

The asymptotic formula (A) for computing a 100(1 - ) per cent confidence interval for true average per cent reduction of caries incidence is applicable when the following are true:(1) The true average caries increment under control treatment is other than zero (µ_c 0); (2) the sample average per cent reduction of caries incidence is defined, that is, when the sample average caries increment under control treatment is other than zero (X_c 0); and (3) the sample sizes (n_c and n_e) are large.

The aymptotic formula (B) for computing a 100(1 - ) per cent confidence interval for true average difference between caries increment of control and experimental treatments is applicable when the sample sizes (n_c and n_e) are large.

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