Re: Unknown mean and known variance? Care to explain a little bit?

The mean value could have changed over time
without a significant change in variance

Thanks! this is a good example of a real life situation.

On Apr 7, 12:51 am, "Phil Holman" <piholmanc@yourservice> wrote:
"sarikan" <serefari...@xxxxxxxxx> wrote in message

news:e9245f79-6059-4157-88eb-94d98fef3324@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Hi,
I've been using statistical methods for a while, but the problem is
some of the usual practices common in many textbooks and courses
sometimes get stuck in my head.
There are a lot of statistical tools that can give you critical
information about your data, and when you take statistics as a tool,
usually people are not really bothered if you really know what the
tool is doing for you or not. (well, most of them)
I'd really appreciate your help about a well known scenario: you can
find it in any statistics book, there is a population with an unknown
mean, and a known variance. I'd love to hear a real life example for
this, and an explanation. We have a population, and we do not know the
mean, but the variance is about average deviation from the mean is it
not? How do we know the spread of a population without knowing the
point it is spread around?
Maybe I'm a little bit confused, but I'd really like to get a little
help

Yes it is a strange situation but it follows a logical sequence when
learning the material. The mean value could have changed over time
without a significant change in variance. With the variance alone, a
confidence interval can be determined from a sample with a specified
level of confidence that the true population mean is contained in the
interval. The bigger the sample, the narrower the confidence interval.

Example: the variance of adult male height is 6.25. A random sample of
100 adult males has a mean height of 70 inches. What is the 95%
confidence interval? Is this significantly different from a mean height
of 69 inches back in 1960?

Later, the student learns about t-tests and the more common scenario of
determining a population mean from sample data only.

Phil H

.

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