Confidence intervals: Imagine you asked 50 customers how satisfied they were with...

fireblade274

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Oct 15, 2015
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So I am taking my first math class in 4 years at college; Behavioral psyc stat, but so far it is just a statistics class, and I HATE it. My teacher breezes through everything, and that coupled with my inability to comprehend this stuff makes everything worse. I'm quite lost in my class, and am going to tutoring tomorrow, but it is after my quiz tomorrow. The quiz is on calculating confidence intervals.

I have been looking online for ways to find them, but they are leaving out tasks that I know we went over in class, and it very much confuses me, and I don't even understand the things we do go over in class. Take this for example, which I found online. It describes how to find confidence intervals:

Imagine you asked 50 customers how satisfied they were with their recent experience with your product on an 7 point scale, with 1 = not at all satisfied and 7 = extremely satisfied.

  1. Find the mean by adding up the scores for each of the 50 customers and divide by the total number of responses (which is 50). If you have Excel, you can use the function =AVERAGE() for this step. For the purpose of this example, I have an average response of 6.
  2. Compute the standard deviation. You can use the Excel formula = STDEV() for all 50 values or the online calculator. I have a sample standard deviation of 1.2.
  3. Compute the standard error by dividing the standard deviation by the square root of the sample size: 1.2/ √(50) = .17.
  4. Compute the margin of error by multiplying the standard error by 2. 17 x 2 = .34.
  5. Compute the confidence interval by adding the margin of error to the mean from Step 1 and then subtracting the margin of error from the mean:

    5.96+.34=6.3
[FONT=Arial, Helvetica, sans-serif] 5.96-.34=5.6[/FONT]

[FONT=Arial, Helvetica, sans-serif]If I had this in front of me I could probably figure it out during the quiz, but it makes NO mention of Z-scores and T-tables, which I know we went over in class and need to use on the quiz because he told us to print out a T-table. This is what makes everything so freaking confusing for me. We talk about Mu, and that wasn't even mentioned in the above explanation. I don't even know what Mu is other then a Pokemon! And everything just goes way over my head. Standard deviation, standard error, margin of error, cumulative frequency, Intervals... It = disparity on myself.

[/FONT]I don't even know exactly what question im asking. Can someone clear things up for me? Where do zScores and T-tables come in? What is Mu? What Is the O variable that looks like a sideways Q that I'm doing a terrible job at explaining? Why are there different ways of computing confidence intervals, and what way does it look like our teacher is teaching us? He gave us the equation CumF = Xbar +- Z(O subscript Xbar) the O has a little dash thing coming out the top going right.

After we find the confidence intervals for a problem, we need to describe whether it determines null hypothesis or alternative hypothesis, and we need to say it in words. He told us if we don't use words, we will get a fat zero on the quiz. HOW RIDICULOUS IS THAT. I feel like im going to die tomorrow. Its a combination of me sucking at math, and my teacher sucking at teaching math. Can anybody help me and shed some light :(
 
Imagine you asked 50 customers how satisfied they were with their recent experience with your product on an 7 point scale, with 1 = not at all satisfied and 7 = extremely satisfied.

  1. Find the mean by adding up the scores for each of the 50 customers and divide by the total number of responses (which is 50). If you have Excel, you can use the function =AVERAGE() for this step. For the purpose of this example, I have an average response of 6.
  2. Compute the standard deviation. You can use the Excel formula = STDEV() for all 50 values or the online calculator. I have a sample standard deviation of 1.2.
  3. Compute the standard error by dividing the standard deviation by the square root of the sample size: 1.2/ √(50) = .17.
  4. Compute the margin of error by multiplying the standard error by 2. 17 x 2 = .34.
  5. Compute the confidence interval by adding the margin of error to the mean from Step 1 and then subtracting the margin of error from the mean:

    5.96+.34=6.3

If I had this in front of me I could probably figure it out during the quiz, but it makes NO mention of Z-scores and T-tables....
Why should it "make mention of" these topics, when they are not necessary? How did you get as far as studying Z-scores without first learning about finding arithmetical averages and computing standard deviations?
 
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