View Full Version : Confidence Intervals

04-17-2008, 07:34 PM
I was hoping that someone can help to explain exactly what this means. I was able to do the problem but do not understand what the answer actually means. Thanks

mean is $39,395.69
~ is $20,023.69
had to find confidence intervals at 90, 95 and 99%

got CI is 90% is +/- $3,293.88 so TPM is $36,101.12 to $42,688.880
95% is +/- $3,924.51 so TPM is $35,470.49 to $43,319.51
99% is +/- $5,157.92 so TPM is $34,237.08 to $44,552.92

Can anyone please explain what these numbers mean, THANKS is advance :o)

04-18-2008, 11:47 AM
I'm guessing that "$39,395.69" is a SAMPLE Mean.

Your intent is to say something about the POPULATION Mean, based on your sample data.

A 90% Confidence Interval indicates that the POPULATION Mean is likely to be in this interval with 90% confidence. If you observe the population means from many similar populations, you should be happy with a failure rate of less than 10%. The only problem with the words "confidence" and "failure" is that we do not KNOW the population mean, so we cannot say if we hit the interval or not.

Clear as mud?