# Statistics question: What % must I survey to ensure validity? **URL:** \ **Category:** Factual Questions\ **Created:** [July 11, 2002, 4:44pm UTC](https://boards.straightdope.com/t/statistics-question-what-must-i-survey-to-ensure-validity/118442 "2002-07-11T16:44:24Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Mars\_Horizon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mars_horizon/32/2804_2.png) [@Mars\_Horizon](https://boards.straightdope.com/u/Mars_Horizon)\ **Post date:** [July 11, 2002, 4:44pm UTC](https://boards.straightdope.com/t/statistics-question-what-must-i-survey-to-ensure-validity/118442/1 "2002-07-11T16:44:24Z")
I have an urgent need for information, and I hope the Teeming Millions can help. I need to determine the opinions of an organization of about 18,000 people. I want my results to be valid, i.e., be a relatively reliable representation of the attitudes of the group. How many people (out of 18,000) must I send my survey to, to ensure a valid response? Is there a flat percentage that is generally accepted? ---
**Author:** ![SmackFu](https://avatars.discourse-cdn.com/v4/letter/s/53a042/32.png) [@SmackFu](https://boards.straightdope.com/u/SmackFu)\ **Post date:** [July 11, 2002, 5:10pm UTC](https://boards.straightdope.com/t/statistics-question-what-must-i-survey-to-ensure-validity/118442/2 "2002-07-11T17:10:40Z")
[Sample size calculator.](http://www.surveysystem.com/sscalc.htm) It isn’t a flat percentage. And be careful mailing surveys. A lot of people won’t return them, and the people that do won’t necessarily be an accurate sample. ---
**Author:** ![alice\_in\_wonderland](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alice_in_wonderland/32/176_2.png) [@alice\_in\_wonderland](https://boards.straightdope.com/u/alice_in_wonderland)\ **Post date:** [July 11, 2002, 5:16pm UTC](https://boards.straightdope.com/t/statistics-question-what-must-i-survey-to-ensure-validity/118442/3 "2002-07-11T17:16:38Z")
I think if you get a 5-10% _response rate_ you’ll be doing ok for a population that size. However, if it’s a self administered questionaire you’ll have to send to a much larger sample of the group to get that kind of response. ---
**Author:** ![aahala](https://avatars.discourse-cdn.com/v4/letter/a/a88e4f/32.png) [@aahala](https://boards.straightdope.com/u/aahala)\ **Post date:** [July 11, 2002, 6:22pm UTC](https://boards.straightdope.com/t/statistics-question-what-must-i-survey-to-ensure-validity/118442/4 "2002-07-11T18:22:06Z")
If your purpose is to get a reasonably accurate percentage of the number of people in your population believing statement “X” or holds view “y”, mailing the survey out is a waste of time. All you find out is the percentage of people who RETURNED the survey held such a position or view. No statements can be accurately made of the population as a whole, unless you KNOW the propensity of each type of viewholder in returning the survey. ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [July 11, 2002, 6:26pm UTC](https://boards.straightdope.com/t/statistics-question-what-must-i-survey-to-ensure-validity/118442/5 "2002-07-11T18:26:18Z")
Just for the record, things like margin of error and all that depend only on the sample size, not the sample size as a percentage of the total population. ---
**Author:** ![Mars\_Horizon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mars_horizon/32/2804_2.png) [@Mars\_Horizon](https://boards.straightdope.com/u/Mars_Horizon)\ **Post date:** [July 11, 2002, 7:26pm UTC](https://boards.straightdope.com/t/statistics-question-what-must-i-survey-to-ensure-validity/118442/6 "2002-07-11T19:26:43Z")
A big THANK YOU to all of you. 🙂 ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 11, 2002, 7:33pm UTC](https://boards.straightdope.com/t/statistics-question-what-must-i-survey-to-ensure-validity/118442/7 "2002-07-11T19:33:46Z")
> [@](#): > > Just for the record, things like margin of error and all that depend only on the sample size, not the sample size as a percentage of the total population. Not true. If my population of interest is my immediate family, and I survey four people, I’ve got zero margin of error. ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [July 11, 2002, 7:36pm UTC](https://boards.straightdope.com/t/statistics-question-what-must-i-survey-to-ensure-validity/118442/8 "2002-07-11T19:36:16Z")
OK, fine, but we don’t usually deal with small populations like that. ---
**Author:** ![aahala](https://avatars.discourse-cdn.com/v4/letter/a/a88e4f/32.png) [@aahala](https://boards.straightdope.com/u/aahala)\ **Post date:** [July 11, 2002, 8:17pm UTC](https://boards.straightdope.com/t/statistics-question-what-must-i-survey-to-ensure-validity/118442/9 "2002-07-11T20:17:07Z")
I might add, Marrs could send out a few hundred surveys, making sure each of the 18,000 had an equal chance of being included in the sample and keep track of the responses and who didn’t respond at all. Then contact virtually all those who didn’t. He couldn’t use mathematical or statistical inference, as people might answer differently by mail or by phone call, but he possibly could get a sufficient level of knowledge for his purpose.