# Determining Sample Size for Medical Device Component Validation

#### Romvill2002

##### Involved In Discussions
Hello All,

I have a bio statistician who helped me figure out the sample size with calculations below.
Can you interpret below determination of sample size. What would be the confidence level if 1 out of 10 samples failed? what does a rejection of 1(out of box failure) sample mean?

Sample size of 10 was purposed by test engineers for the verification of the pressure switch and regulator pressure components replacement in FACSCelesta system. There were no historical or pilot data available for sample size estimation prior to the verification study. Therefore by using the vendor specification for pressure switch along with BD internal verification acceptance criteria, the power for the purposed sample size of 10 is estimated to ensure there is sufficient power to meet the test requirement with the following assumptions.
Vendor Pressure switch specification: 10 psi ± 1
BD pressure switch verification criteria: 10 psi ± 5
Assuming the vendor also tested with sample size of 10, with mean center at 10 psi, the largest standard deviation is estimate to be 1.35 .

N Mean StDev SE Mean 95% CI T P
10 10.000 1.350 0.427 (9.034, 10.966) 0.00 1.000

Using theoretical calculated standard deviation of 1.35, the power for the purposed sample size of 10 is estimated to be greater than 99% assuming the difference of the test is at most half of allowable drift (2.5) from the target mean of 10 psi with alpha of .05
Calculating power for mean = null + difference
α = 0.05 Assumed standard deviation = 1.35

Sample
Difference Size Power
2.5 10 0.999308

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