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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

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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.
.

Jan 05, 2017 | Office Equipment & Supplies

1 Answer

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)
= 100 / 8
= 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

374.5 to 325.5
.

Dec 11, 2015 | Institute of Mathematics and Statistics...

2 Answers

Construct a 99 confidence interval for the population mean if my sample mean is 125, and Std Dev is 8, and population size is 64


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
.

Dec 10, 2015 | Institute of Mathematics and Statistics...

1 Answer

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


Manual is available in PDF format from here

http://docslide.us/download/link/dca-operators-guide


http://docslide.us/download/document/?id=%2FJKJQj2KkZIjS9Tn4Jm5CAbRibVv%2BGl%2BT9wi7I03ZyGSjZf8c1bXQnPy2%2FSc3BFIu8t3mvccp4VXj23OQyX8pQ%3D%3D

DCA Vantage Operator's Guide 109
Troubleshooting
E22 - Optical
reading is out
of range
A Sample or Reference
channel reading taken
during an Air
measurement is too
high.
1. Discard the sample.
2. Run an optical test.
3. If you are unable to run an
optical test, contact your local
technical support provider.
E23 -
Excessive
noise on the
Sample
channel
The standard deviation
of the 16 readings at the
Sample channel for Dark
or Air reading is too
large.
1. Discard the sample.
2. Run an optical test.
3. If you are unable to run an
optical test, contact your local
technical support provider.
E24 -
Excessive
noise on the
Reference
channel
The standard deviation
of the 16 readings at the
Reference channel for
Dark, Air or Sample
reading is too large.
1. Discard the sample.
2. Run an optical test.
3. If you are unable to run an
optical test, contact your local
technical support provider.
E26 -
Excessive
noise in sample
reading
The standard deviation
of the 16 readings at the
Sample channel during a
reading taken is too
large in Sample read
position.
1. Discard the sample.
2. Run an optical test.
3. If you are unable to run an
optical test, contact your local
technical support provider.
E27 -
Excessive
Lamp Drift
The change in mean
signal between
successive Air readings
is too large at either the
Sample channel or the
Reference channel.
1. Discard the sample.
2. Run an optical test.
3. If you are unable to run an
optical test, contact your local
technical support provider.
E30 - Thermal
control system
error - low
The temperature
measured by one of the
cartridge holder
thermistors is ?2?C.
1. Discard the sample.
2. Restart the system.
3. If you are unable to perform a
successful restart, contact
your local technical support
provider.
E

Sep 21, 2015 | Siemens Dishwashers

1 Answer

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!

May 03, 2014 | Audio Players & Recorders

1 Answer

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.

Apr 18, 2012 | Casio FX-9750GPlus Calculator

1 Answer

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.

Apr 18, 2012 | Casio FX-9750GPlus Calculator

1 Answer

Finding standard deviation of samples!!


34 σ+
39 σ+
32 σ+
36 σ+
30 σ+
33 σ+
2nd ÷ (σxn)

Jun 02, 2009 | Texas Instruments TI-30XA Calculator

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