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January 4th, 2016, 12:08 AM   #1
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Grandpa's ice cream company

Grandpa's ice cream company makes ice cream sandwiches, ice cream bars, and half-gallon containers. The company wants to set up a quality control by regularly testing their ice cream products. Discuss each of the following sampling procedures and whether there is bias in the selected samples.

a) Every hour of production they pick a 10-minute interval to select five itmes from each of the product lines to test. The 10-minute interval is determined by rolling a die. If they roll a 1, they test during the first 10 minutes. If they roll a 2 they test during the second 10 minutes and so forth.

b) They select 10 items from each of the product lines at 5 PM every day

c) Each day, the names of ice cream sandwiches, ice cream bars, and half-gallon containers are written on pieces of paper and placed in a hat. The product that is selected first is tested at 8 AM. The product that is selected second is tested at 12 PM and at 4 PM the remaining product is tested. A product is tested by picking 10 items at the given hour.

My attempt:

Method (a) produces a large sample and there's an element of randomness in the selection. It appears to be the best among the three methods

Method (b) produces a small sample and if the ice cream machine fails at around 5 PM this will produce a sample that is not representative

Method (c) has a random element but the sample size is smaller than in (a) and at the specified times, the machine may fail

Am I correct? What do you think? Thanks
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