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In one recent online forum, a Six Sigma Black Belt asked a question about validating samples—how to ensure that when they are taken, they would reflect (i.e., represent) the population parameter. His purpose: to understand the baseline for a project. He said he had six months of data regarding cycle times for handling maintenance tickets.
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Among the early suggestions to the query were an assortment of options, including cross validation using regression (comparing randomly selected subsets) and t-tests on small samples. Another person suggested testing the data for normality: “Then any sampling technique will do,” he claimed.
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Comments
I like that one
Average phone number? Rip - good one!
But seriously I sometimes wonder - assuming competent managers and employees, shouldn't we be able to figure out most things just by looking at the time series? A group responsible for maintenance ticket turnover time or nurse response time should be able to understnad when they are doing well and when not and also why by virtue of the fact that they work there. Insiders should know. Outsiders need fancy analysis.
Maybe...
If they are using a time series, then they are ahead of the game. With a stable process, though, I still want the process behavior chart, so I can tell when assignable causes happen. It's not fancy analysis, just an XmR chart.
Go down Sampling
Based on my work experience, I'm more familiar with Pierre Gy's sampling theories, though criticized they can be. In any case, I do much appreciate a professional raising this issue: effective sampling is far from being AQL tables and ISO 2859 only. Thank you.
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