Provide a point and interval estimate (95% CI) for the interlaboratory standard deviation of mean zone diameters for each type of control strain, assuming each laboratory uses different media to perform the susceptibility tests?

Microbiology

A nine-laboratory cooperative study was performed to evaluate quality control for susceptibility tests with 30-μg netilmicin disks [6]. Each laboratory tested three standard control strains on a different lot of Mueller-Hinton agar, with 150 tests performed per laboratory. For protocol control, each laboratory also performed 15 additional tests on each of the control strains using the same lot of Mueller-Hinton agar across laboratories. The mean zone diameters for each of the nine laboratories are given in Table 6.11.

Table 6.11 Mean zone diameters with 30-μg netilmicin disks tested in nine separate laboratories

 

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Type of control strain S. aureus P. aeruginosa Different media E. coli Laboratory Different media Common medium Different media Common medium Common medium 27.5 24.6 25.3 28.7 25.4 24.8 24.6 23.8 23.9 20.1 16.7 18.4 16.8 21.7 24.2 25.0 17.0 21.1 25.4 25.4 17.1 18.2 29.8 26.7 27.5 28.1 31.2 20.1 20.3 22.8 24.8 25.7 26.8 25.3 16.7 19.2 18.8 23.0 26.8 24.7 25.2 G 27.1 24.3 24.9 26.2 26.3 19.9 19.3 18.1 19.2 26.5 25.1 24.3 25.4 н < mO O wuO I -