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Riley Research
10200 SW Eastridge
Suite 120
Portland, OR 97225
503-222-4179


Sample Calculator

How many people do you need to talk to to get a margin of error you are comfortable with? Consult our handy calculator and find out!

Listed below are few terms you will need to understand before using the sample size calculator:

Confidence Level: The percentage value that tells how confident a researcher can be about being correct. A 95% confidence level is a generally acceptable level of confidence and is most typically used and accepted within the research industry. Which means that if a study were conducted 100 times, answers would be within the margin of error 95 out of 100 times.

Margin of Error / Confidence Interval: Assumes that you have a random sample. The margin of error for a typical survey is +/- 5%. This means that results may vary as much as five percent in either direction. The margin of error for sub-samples (i.e. men versus women), is based on the number in that sub-sample.


Population Size: The population size is the universe from which you are taking your sample. If the population size is very large or unknown, leave this field blank.

DIRECTIONS:
  • Choose a confidence level
  • Enter an acceptable margin of error (between .1 and 50 - leave off % sign)
  • Enter population (if known)
    Click on "calculate"
  • This calculator requires Internet Explorer 3.0 or later or Netscape 3.0 or later or a compatible browser. Leave the population box blank, if the population is very large or unknown.
CAUTION: Sampling error is only one source of bias. Contact us to discuss other possible sources of bias (i.e. question bias).

Determine Sample Size

Confidence Level: 95% 99%
Margin of Error/Confidence Interval:
(Do not include % sign)
Population:
Sample size needed:

(This sample size calculator was created by Creative Research Systems.)
Sample Size: n=

50

100

200

300

400

600

800

1,000

Margin of Error*:(+/-)

14.2%

10.0%

7.1%

5.8%

5.0%

4.1%

3.5%

3.2%

The margin of error for a poorly designed survey: +/- 100%

* Based on a 95% level of confidence; assumes a random sample and worst-case (50/50) response.  If this does not make sense, it's time to call Riley Research.

 

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