SAMS has embarked on a quality improvement effort. Its first project relates to

Question

SAMS has embarked on a quality improvement effort. Its first project relates to maintaining the target upload speed for its internet service subscribers. Upload speeds are measured on a standard scale in which the target values are 1.0. Data collected over the past year indicated that the upload speed is approximately normally distributed, with a mean of 1.005 and a standard deviation of 0.10. Each day, one upload speed is measured. The upload speed is considered acceptable if the measurement on the standard scale is between 0.95 and 1.05.

The objective of the operations team is to reduce the probability that the upload speed is below 1.0. Should the team focus on process improvement that increases the mean upload speed to 1.05 or on process improvement that reduces the standard deviation of the upload speed to 0.075? Explain.

Explanation / Answer

1) if team increase mean to 1.05

P(X>1)=1-P(X<1) =1-P(X<(1-1.05)/0.1)=1-P(Z<-0.5) =1-0.3085-0.6915

and if standard deviation of the upload speed reduces to 0.075

P(X>1)=1-P(X<1) =1-P(X<(1-1.005)/0.075)==1-P(Z<(-0.0667))=1-0.4734=0.5266

hence it seems it is better to increase mean speed then to reduce std deviation

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