STAB22H3 Chapter : STAB22-C20.docx
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STAB22H3 Full Course Notes
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Huge pieces of metal that are used as structural parts for cars and planes. Problem: if they crack while they are manufactured, they must be remade, or recycled, but recycling costs too much $ Before changes were made to manufacturing, only 80% free of cracks. After changes, 400 ignots were sent for manufacturing and out of which 83% free of cracks. Has the cracking rate really reduced, or was this by chance? p531. Recall: each random sample has diff. prop. of cracked ignots (b/c there is variation from one sample to another) The above qn, and ex"s below are answered by testing hypotheses about models: Hypotheses = working models that are adopted temporarily. To test whether changes made to manufacturing process really did improve cracking rate, assume that: It made no difference, & so any sort of improvement is really just random fluctuation (sampling error) States that prop. of cracks really is still 20%
