Question

You are the quality assurance person working an assembly line at a TV manufacturing plant. They produce 1000 TV’s a day. IF THE TV’S ARE ALL THE SAME MODEL, WHAT PERCENTAGE (think about the cost of testing) WOULD YOU TEST (WHY?) AND HOW WOULD YOU SELECT THEM (Don’t just say “randomly” – How do you do it randomly?) If the inspector were lazy, how would they likely do it as a “convenience” sample? Lastly, if the 1000 TV’s were 4 different models, how would you sample then and what type of sampling would this be?

#2. You are going out to eat. There are three shopping malls nearby and each has up to five restaurants (these restaurants are all different styles: e.g., Italian, Chinese, French). Here are their customer SATISFACTION ratings on a scale of up to five +’s (highest satisfaction). WHAT ASSUMPTIONS ARE YOU MAKING REGARDING WHAT “SATISFACTION” MEANS? Mall 1 Mall 2 Mall 3 (a) ++++ (a) +++ (a) +++++ (b) ++++ (b) ++ (b) ++++ (c) ++++ (c) +++ (c) +++ (d) ++ (d) + (e) +++

#3. (a) What type of data and scale are involved here? (b) Which Mall Restaurant did you pick? WHY? (c) What issues could you encounter with your pick once you got there?

#4. What is a CONVENIENCE SAMPLE? Give an example of one and explain when it might be actually useful in giving a picture of the entire population, and what could be misleading about it.

#5. You can find 20 RANDOM NUMBERS in a Table or you can generate them with software like Excel. The Excel functions are “RAND” and “RANDBETWEEN”. With “Randbetween” you simply input how many numbers you want, the number of digits you want in your random number and the range of values you want those numbers to fall between. For example you may want twenty, 2-digit numbers that fall between 00 and 100 (like “34”).

TWO CONSIDERATIONS: (1) You must systematically use the random numbers in the Table or the ones generated. You don’t “skip around” because that could un-randomize the values. (2) Let’s say you want 1000 names from a 50 page phone book. You reach the end of the book with your systematic selection and only have 800 names. What do you do? Simple: start over in the book (loop). For example, if you were selecting names from every 15th page and you reached the end of the book after only 8 pages, then start over on page 7 of the same book.

One source of random numbers is the Greek symbol “π” and its numerical value used in geometry is 3.141592653589793238462643383. . . (ignore the decimal between 3 and 1) and you have THIS string of random numbers: 3141592653589793238462643383. USE THIS STRING (and loop it) to generate twenty, 3-digit (e.g. 314) random numbers AND EXPLAIN how you did it.

Answer 1

As Protocol, I shall be answering only the four parts of this exaustive questioniarre.

1. The TVs are of the same make and hence there will be 1000 identical objects.

Now selection of sample will depend on:-

1. Confidence level

2. Confidence interval and

3. Population Size

Necessary Sample Size = (Z-score)² * StdDev*(1-StdDev) / (margin of error)² ; (Z score at 95% is 1.96)

Assuming the 95% confidence level for a margin of erro of 55( CI) , for a population of 1000 identical TVs

the sample size has to be equal to 278.

In percentage it will be equal to 27.8%.

For a lazt examiner- He will tend to take sample once in a while and hence he will take all samples at once during the entire process.

If 1000 TV are of 4 models of 250 each then

At 95% confidence and 5% margin of error ,we need to have a sample of 152 TV of each model examined.

Thus for 1000 TVs ,we shall have to examine 608 TV (=60.8%).

This is called as cluster sampling.

2).

.

3).It is a qualitative data which uses relative scale for rating. Mall ! has to be chosen since it encompasses data from all the five (variables) the restaurants .Thus we can compare all variables only if we pick mall 1.

4). A convenience sample is one of the main types of sampling methods in which we cant assign a certain probablity to its elements A convenience sample is made up of people who are easy to reach. Consider the following example. A pollster interviews shoppers at a local mall. If the mall was chosen because it was a convenient site from which to solicit survey participants and/or because it was close to the pollster's home or business, this would be a convenience sample.

It can be useful for consideration of population when:-

1. The number of variablesi n sampling is minimal

2.The probability distribution is not too high.

3. The condition of sampling remains constant.

It can be misleading since extrapolation of sample results cant be valid on the population.