| Sample
Size Calculator - Proportions
Getting the correct sample size is critical to many projects.
Our sample size calculator (for proportions) makes calculating
your sample size simple and quick.
Use this calculator (for proportions) if you are answering a
question like "How big a sample do I need to find out what
proportion of customer queries get answered by our back-office
function within Service Level?"
Use the other
calculator (for means) if you are answering a question like "How
big a sample do I need to find out how long it takes our back-office
function to answer a customer query?"
Three things affect your sample size.
- How confident you want to be in the result (The Confidence
Level, expressed as 90%, 95% or 99%)
- How accurate you need the result to be (expressed in +/- 'n'
units. For example if you want to know what proportion of
customers get responded to within Service Level to within +/- 3%,
you would enter 0.03 in the 'Acceptable Error' field). The
Acceptable Error of the Estimate is sometimes called the
Confidence Interval.
- Based on previous data or your knowledge of the process, what
proportion of customers got responded to within Service Level. So,
for example, if previous research showed that 91% of customers
were responded to in Service Level, you would enter 0.91 in the
Data Proportion field.
If you need to be very confident in the results (e.g. 99%) and for
them to be highly accurate (say +/- 1%) then you will require a
large sample to give you this degree of confidence and accuracy.
However if you don't need to be so confident in the result (e.g.
95%) and it's not necessary to be so accurate (say +/- 4%) you will
require a much smaller sample.
Sample size is usually a mixture of desired confidence and accuracy
balanced by the cost of obtaining the sample.
The most pragmatic approach is to put the Confidence Level and
Acceptable Error you would really want into the sample size
calculator and see what the recommended sample size is. If it is too
large, try adjusting the Confidence Level and Acceptable Error
values until you have a practical sample size.
The calculator defaults to 95% Confidence Level and 1 unit (0.01) of
Acceptable Error. You can change these to suit your needs.
If you would like to learn more about Lean and 6 Sigma tools and
methodologies, click here for
open training courses,
or in-house training courses.
If you cannot see the sample size calculator, check whether your
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Player installed.
Note: aorist consulting ltd. provides tools and examples for
illustration only, without warranty either expressed or implied.
This includes, but is not limited to, the implied warranties of
merchantability or fitness for a particular purpose.
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