iPhones Suppose 1000 iPhones are produced at a factory today. Management would l
ID: 3375035 • Letter: I
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iPhones Suppose 1000 iPhones are produced at a factory today. Management would likc to ensure that the phones' display screens meet their quality standards before shipping them to retail stores. Since it takes about 10 minutes to inspect an individual phone's display screen, managers decide to inspect a sample of 20 phones from the day's production. Explain why it would be difficult for managers to inspect an SRS of 20 iPhones that are produced today. 17. (a) (b) An eager employee suggests that it would be easy to inspect the last 20 iPhones that were produced today. Why isn't this a good idea? Another employee recommends a different sam- (c) iPhones produced. Inspect that phone and every fiftieth iPhone produced afterward. (This method is known as systematic random sampling.) Explain carefully why this sampling method is not an SRS.Explanation / Answer
(a) out of 1000 iPhones produced if a random sample of size 20 is drawn then the sample size 20 is quite less compared to total production of the day. In an SRS of 20 sample out of 1000 units each of 20 units has probability 1/1000 =0.001 of being selected , which is very less.
(b) if the last 20 phones produced are inspected then this sample is not a representative of the total production.
Because there may be a change in the production process ( may be machine is not working efficiently) in the end of the day. Any change in the production process influences the quality specification of a certain numbers of successively produced iPhones .The manager wants to ensure that all 1000 iPhones produced meet the quality specification of the display screen. So,inspecting the last 20 phones produced does not ensure whether the whole day's production meet the quality specfication.
(c) SRS is a probability sampling in Which every member of the population has Equal probability of being included in the sample.
Systematic sampling is partly probabilistic and partly non probabilistic sampling. This sampling method is probabilistic since the first member of the sample is selected at random from first 50 units(each of first 50 population units has Equal chance of being selected as first sample unit) . This method is non probabilistic since the other units in the sample are fixed(every fiftieth member is selected after the first unit is selected ) by the choice of the first unit.
So, systematic random sampling is not an SRS.
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