Report and Calculator Package
Sample size questions are common but complex. This report and calculator makes the concepts easier to understand and implement.
27 Page Guide on Computing Sample Sizes
This guide has a five-step process for finding the right sample size for your survey. It includes four detailed example questions as well as five practice exercises and answers, and show you how to find sample sizes for the Net Promoter score.
Sample Size Calculator for Rating Scales
Just enter your desired level of precision (e.g. half-a-point) and the number of response options and the calculator provides you with the sample size. It uses industry benchmarks if you don't know the standard deviation (explained in detail in the 23 page report).
Sample Size Calculator for Binary Responses
Do users agree or disagree with statements, are they promoters or detractors? Binary responses (only two option responses) are one of the most common response types in surveys. Just enter the desired margin of error (and optional percentage) and the calculator gives you the needed sample size.
Simple Instructions for using the calculator
The report walks you through a five step process (through four detailed examples) and allows you to intelligently frame sample size questions by understanding the important concepts of precision, confidence and variability.
Plenty of Practice questions available to match your specific need
With five practice questions and detailed answers you should have no problem understanding how the formulas generate the results. No need to dig through old college statistics textbooks for arcane explanations.
Deatiled explanations of the formulas
No one likes to memorize formulas. The guide shows you the basic components of the sample size formulas, how they are derived from confidence interval formulas and some short-cuts for quickly and accurately computing sample sizes.
Confidence Interval for Binary Responses
As a bonus, I've included a confidence interval calculator for binary responses. This way, you can both predict your sample size and report your margin of error after you collect your data.
Confidence Interval for Rating Scales
As a bonus I've also included two confidence interval calculators for rating scale data. This allows you to generate standard deviation estimates from past data and and report your margin of error after you collect your data (using both summary data and raw data).
Estimating a Needed Sample Size from a Sample Response Rate
Use this calculator to estimate the total number of invites you need to send out in order to maintain a desired margin of error (e.g. 5%).
Confidence Interval for a Net Promoter Score
A Net Promoter Score is based on two dependent proportions (promoters and detractors). This confidence interval calculator uses the most accurate method for any sized sample and it works when the NPS is negative.