Your best estimate of the number of shoppers who enter your store and make a pur

Question

Your best estimate of the number of shoppers who enter your store and make a purchase is around 20%, but you want to do a study to accurately estimate it. You want to be able to estimate within a margin of error of 3% with 90% confidence. 5, what are the following: MoE, z, and /T? (whether you use or depends on whether you are calculating sample size for a mean or a proportion) Based on your answers in question 5, calculate the minimum sample size needed. If you want a smaller margin of error (e.g., 296), will it increase or decrease the sample size? Assume that you have no idea what the percentage will be for shoppers that make a purchase. What value should you assume the percentage is when calculating the minimum sample size? 6. 7. 8.

Explanation / Answer

Question 5

(a) MOE = 0.03

Z = 1.645 (for 0.05 confidence level)

p^ or pi = 0.20

(B) Sample size needed. Let say it is n

standard error of proportion SE = sqrt(0.20 * 0.80/n) = 0.4/ n

so 0.03 = 1.645 * (0.4/n)

n = 21.933

n = 481.07 or say 482

(c) we will decrease the sample size if we need smaller margin of error.

(d) to calculate minimum sample size we will use the percentage for shoppers to make a purchage as 0.5 as it will provide the minimum value of n that shall be needed.

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