Table of Contents
Confidence Interval By James Grow
Measurement Criteria
Some assumptions are made
s for systolic Blood pressure is 20
Average measured pressure is 130
s decreases with the number of samples taken
s for seven measurements
95.4% of sample are within 2 s
The margin of error with 95% confidence is 2s
This interval runs from 115-145
Most sample(95%) will lie within this interval
The larger the confidence more will lie within the interval
However, a few will not (5%)
Confidence Levels
Duracelle batteries last longer
is the clam. How to prove it
Here the batteries are packaged
Test a random sample of batteries
In the Rack
A steady current is drained
If done in toys, variability due to toys can effect results
For a 95% confidence
1.960 standard deviations on both sides of mean are needed
For a confidence level of 99%
2.576 standard deviations on both sides of the mean are needed
To calculate the confidence interval this formula is necessary
For forty batteries the mean life time is 360 minutes with s =23
Giving the results
68% confidence level with 1s
95% confidence with 2s
A small standard deviation is good
However, if it is large
The only way to decrease the uncertainty is to increase n
It takes 4 times the number of measurements to half the interval
The square root sign takes its toll
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Author: Compaq User
Email: Grow@adm.njit.edu
Home Page: http://www-ec.njit.edu/~grow/statisti.htm
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