Self-study
Quality control investigator: Support Upon testing samples of products from our supplier that were sent by our field inspectors from various manufacturing locations, our laboratory discovered that over 20 percent of the samples were defective. █████ ███ ████████ ██ █████████████ ████████ ██ █████ ███ ████ ██ ███████ █████ █████ ██ ████████████ ███ ██ ██ █████ █ ████████ ██ ███ ████████ ███ ████████ ████ ███
Summarize Argument
The author concludes that the supplier’s rate of defects for items it manufactures is not below 5 percent, as the contract requires. This is based on the fact that after testing samples of products sent by field inspectors from various manufacturing locations, the lab found that over 20% of the samples were defective.
Identify and Describe Flaw
The author assumes that the rate of defect in the samples sent by field inspectors is representative of the rate of defect in the overall set of products manufactured by the supplier. This overlooks the possibility that the samples selected have a higher rate of defect than the average product (perhaps because the field inspectors might be looking for potentially defective items).
20.
The reasoning in the quality ███████ ██████████████ ████████ ██ ██████ ██ ████ ███ ████████
a
bases its conclusion ██ ███ █████ █ ██████ ██ █████ ██████ ██ ███ ██████████
We have no reason to think the sample of items sent by the inspectors is too small. In order to pick (A), we need some textual hook in the stimulus to suggest the sample size is too small.
b
presumes, without providing ██████████████ ████ ███ █████ ██████████ ████ ████ ██ ██████ ██ ██████ █ █████████ ████ ███ ███████ ██ ████ ████ ██ ██████ █ ████████████ ████
The assumption is that rate of choosing defects did not exceed the actual defect rate. (Ex. Actual rate is 25% defects, and inspectors chose defective items 25% of the time, nondefect 75%.) This doesn’t require chance of choosing defect to be equal to choosing nondefect (50-50).
c
overlooks the possibility ████ █ ███ ██ ███ █████████████ █████ ███ ███████████ ███ ████ ██ ███ █████████ █████
This doesn’t undermine the argument, because we have no reason to think that a few sites being responsible for most defects would skew the defect rate in the inspectors’ sample. We have no reason to think the inspectors disproportionately picked items from these few sites.
d
overlooks the possibility ████ ███ █████ ██████████ ████ ██ ██████ █████ ███ ███████ ████ ████ ███████ ███ █████████
This undermines the argument, because it shows that the sample selected by inspectors might have a higher rate of defect than the average product produced by the supplier. This is why we can’t assume the over 20% defect rate in the sample applies to the overall set of products.
e
presumes, without providing ██████████████ ████ ███ █████ ██████████ ████ ██ █████ ██████ ██ ██████ ██ ████ ██ ███ ███████ █████████████ █████ ██ ███ ████████
The author does assume that the manner in which the inspectors collected items for the sample was not biased in a way that made the defect rate in the sample unrepresentative of the overall defect rate, but this doesn’t require any view about the number of visits.