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Old January 12th, 2009, 09:29 AM
mwe mwe is offline
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Exclamation help me in statistics pls...

The following data values are a simple random sample from a population that’s normally distributed, with σ2 = 4.0 11, 6, 8, 12, and 13. Construct and interpret the 90% and 95% confidence intervals for the population mean. show solution pls..
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Old January 12th, 2009, 10:16 AM
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Originally Posted by mwe View Post
The following data values are a simple random sample from a population that’s normally distributed, with σ2 = 4.0 11, 6, 8, 12, and 13. Construct and interpret the 90% and 95% confidence intervals for the population mean. show solution pls..
Sorry, we do not solve the problem for you - that is your job.

However, I will get you started:

For any confidence interval, call value of the confidence level C (such as 90% or 95%, as in your case). Then the probability that the true population mean (called \mu) lies within a given interval with a confidence level of C is:

P(\bar{x} - z \frac{\sigma}{\sqrt{n}} \leq \mu \leq \bar{x} + z \frac{\sigma}{\sqrt{n}}) where \bar{x}, z, \sigma, n are your mean, z-score, standard deviation, and sample size, respectively.

So your confidence interval is between the points
\bar{x} - z \frac{\sigma}{\sqrt{n}}, \bar{x} + z \frac{\sigma}{\sqrt{n}}

To find a given confidence interval, plug in those values. The z-score will be based on your confidence level. Look them up in a z-table. A 90% confidence interval will exclude 5% of the normal distribution on neither side (a total of 10% excluded). A 95% confidence interval will exclude 2.5% (for a total of 5% excluded).

In other words, for a 90% confidence interval, you say with repeated experiments using the same z-score, sample size, and standard deviation, the true population mean will fall within your intervals 90% of the time.
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