Suppose you are researching the eating habits of people your age. What sampling method could you use to find the percent of students in your grade who eat five servings of fruit and vegetables each day? What is an example of a survey question that does not have bias?
The Answer
Sampling is necessary only when the entire population of interest is either too large to unavailable for polling . But, when sampling is needed, the sample size is calculated from the desired confidence interval of results and the estimated population size.
For small population such as a class it is best to simply obtain answers from all .
Solution : ( a )
Given :
μ = 64
σ = 3.5
a)
μ - 3σ = 64 - 3 * (3.5) = 64 - 10.5 = 53.5
μ - 2σ = 64 - 2 * (3.5) = 64 - 7 = 57
μ - σ = 64 - 3.5 = 60.5
μ = 64
μ + σ = 64 + 3.5 = 67.5
μ + 2σ = 64 + 2 * (3.5) = 64 + 7 = 71
μ + 3σ = 64 + 3 * (3.5) = 64 + 10.5 = 74.5
b)
z-score for 71
= (71 - 64)/3.5 = 2
P(z < 2) = 0.9772
n = 3000 * (1 - 0.9772) = 3000 * 0.0228 = 68.4 ≈ 68
n = 68
For this type of question it is best to be posed as an open ended single response .
I.e., simply ask them that
Do you eat 5 servings of fruit and vegetables each day? Or how many servings of fruits or vegetables do you eat in a day..?