Question about Texas Instruments TI-83 Plus Calculator

# Calculating a 93% confidence interval

If the standard deviation for lifetimes of vacuum cleaners is estimated to be 400 hours, how large a sample must be taken in order to be 93% confident that the marge of error will not exceed 50 hours?

I know that n+(za/2)2 standard devation squared/the margin of error squared. What I don't know is how do I get the 93% confidence which is the z a/2 squared

Posted by on

1 - .93 = .07/2 = .035

Posted on Nov 05, 2008

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Posted on Jan 02, 2017

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### Finding the margin of error with a sample size of 1,040, sample mean=46,239, sample standard deviation=21,000

I'm assuming here that 1,040 means one thousand and forty, not a metric decimal comma.

First we need the Std Dev of the mean value itself. This is

s / sqrt (n) = 21000 / sqrt (1040) = 651.2

Then the confidence interval for the mean value is

mean value ± Z * ( s / sqrt (n) )

where Z is an estimator related to the required confide

CL Z
99% 2.576
98% 2.326
95% 1.96
90% 1.645

So for a confidence of 95% the margin of error for the true value of the mean is

46239 ± 1.96 * 651.2 or
46239 ± 1276.3

that is, the mean of a sample from this process will be in this range to 95% confidence.

The margin of error for a future sample value would be

46239 ± 1.96 * 21000 or

46239 ± 41160

that is, a single sample value from this process will be in this range to 95% confidence.
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### I need to find the a 95% confidence interval estimate for population mean. My SD is 100, sample sz. is 64, and sample mean is 350.

First you need the Std Error of the mean value, a measure of the dispersion of that mean value.

SE = sample std deviation / sqrt (sample size)
= 100 / sqrt (64)
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= 12.5

Then we use a figure for the number of std errors either side of the mean value, which make up a 95 % confidence interval. This is ± 1.96 std errors, from tables of the Normal Distribution.

So the confidence interval is

350 ± 1.96 * 12.5 or

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First you need the Std Error of the mean value, a measure of the dispersion of that mean value.

SE = sample std deviation / sqrt (sample size)
= 8 / ? 64
= 1

Then we use a figure for the number of std errors either side of the mean value, which make up a 99 % confidence interval. This is ± 2.58 std errors, from tables of the Normal Distribution.

So the confidence interval is

125 ± 2.58 * 1 or

127.58 to 122.42
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### I have DCA analyzer from Siemens healthcare and i have problem E24 ,How Can Solve it

Manual is available in PDF format from here

DCA Vantage Operator's Guide 109
Troubleshooting
E22 - Optical
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2. Run an optical test.
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2. Run an optical test.
3. If you are unable to run an
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E30 - Thermal
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### What is deviation standard

The standard deviation is a measure of how "tight" the samples are distributed around your mean.
In layman's terms, a small standard deviation indicates that most of your measurements are in the vicinity of the means; a large standard deviation corresponds to readings that are all over the place.
You could also say that the smaller the SD, the more your mean is representative of the data set.
For a better explanation, just look up Standard deviation on Wikipedia!

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### How do i find sample size?

Count the number of items in the sample whose statistics you're calculating. For example, if you're calculating the mean and standard deviation of five items then the sample size is five.

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### How to get sample size

Count the number of items in the sample whose statistics you're calculating. For example, if you're calculating the mean and standard deviation of seven items then the sample size is seven.

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