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Student's_t_test

Student's_t_test - Control Charts Confidence Interval...

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Control Charts Confidence Interval Student’s “t” test How do we verify accuracy? Quality Control Charts μ is known or assumed ! is known 3 ! action line: 1 in 500 2.5 s action 1 in 100 (99%) 2 ! warning: 1 in 20 (95%) Confidence Interval The standard deviation indicates precision varies with N How close is experimental mean to μ? Theory allows an estimate of the range within which the true value might fall with a given probability The range is called “confidence interval” limits of the range are the “confidence limits”
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t - statistical factor, depends on N and the confidence level desired confidence limit is product of t and the standard deviation of the mean Values of t given in tables for different confidence levels and degrees of freedom Student’s “t” Table range increases with required confidence level range decreases " (N) Example for Confidence limits A soda ash sample is analyzed in the lab. by titation with standard HCl Triplicate determination of Na 2 CO 3 93.50, 93.58, 93.43% Within what range of confidence are you 95% sure that the true value lies?
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Solution for Confidence Limits mean = 93.5%, s = 0.075% Na 2 CO 3 At 95% confidence and 2 degrees of freedom, t = 4.303 – Confidence limit
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