One of the questions I get asked a lot is how big a sample do I need. The information below provides the answer. It gives you a guide to how precise the answers to a survey will be and is a useful tool for me. Hope it gives you some future direction for your planning.

HOW BIG A SAMPLE DO YOU NEED? 

Here’s the answer. You can be 95% confident the results of your survey will be plus or minus the percent point shown in the table below for various sample sizes. This means the range should contain the result in 19 out of 20 times the survey would be repeated. If your survey result is 50%, for example, you can be 95% sure it’s really between 44% and 56% if your sample size is 300.

STATISTICAL SIGNIFICANCE OF SURVEY RESULTS

Sample Size	95% Confidence Tolerance
2,000	+/- 2 percentage points
1,000	+/- 3 percentage points
500	+/- 4 percentage points
400	+/- 5 percentage points
300	+/- 6 percentage points
200	+/- 7 percentage points
100	+/- 10 percentage points

 

Compliments of

Dan Wiese Marketing Research

2108 Greenwood Drive SE

Cedar Rapids, IA 52403

(319) 364-2866

danwiese@mchsi.com