confidence interval-big picture

[IdRatherSleep]

I know how to get confidence intervals and all but for some reason I am unable to see the big picture. "96 people were interviewed for a survey about how many hours they worked, standard deviation was 7.77 hours and the mean was 13.15 hours. Determine a 95% confidence interval."
I did and got 11.6 to 14.7.(What does this mean?)
Then I had to get a 95% confidence level of whether they liked working or not using yes answers as a point estimate. So I did and got .4 to .6(what does this mean or say about the survey, people, etc.)
I hope someone can help as I really want to get a sense about what it is all about, my questions are in parentheses. I already searched around in the web and will continue to do so but I need to know before tomorrow morning so this is why I use the forum. Thanks.

 

[tkhunny]

You do NOT know the actual value. You are estimating the value. The confidence interval expresses variation in your estimate. Calculating an average based on a sample is only an ESTIMATE of the mean. The confidence intervals suggests how good the estimate might be.

 

[idegroote]

95% confidence interval

Hi

the confidence interval in easy terms basically means:

that if a series of samples were drawn and the mean of each calculated, 95% of the means would be expected to fall within the range of 2 standard errors above and 2 standard errors below the mean of these means. So, it gives you information about the difference between the mean of the sample (small group you use for your study) and the population (everyone).

So when you use the 95% confidence interval you could say that there is only a 5% chance that a value of your sample lies outside the "sample mean +/- 2 SD." Another way of saying this is that the probability of obtaining a value that lies outside the confidence interval is 5% or less.