Title: Sample Size Calculator - Confidence Level, Confidence Interval, Sample Size, Population Size, Relevant Population - Creative Research Systems
Headings: Sample Size Calculator
Sample Size Calculator
Sample Size Calculator Terms: Confidence Interval & Confidence Level
Factors that Affect Confidence Intervals
Sample Size
Percentage
Population Size

Content: The 95% confidence level means you can be 95% certain; the 99% confidence level means you can be 99% certain. Most researchers use the 95% confidence level. When you put the confidence level and the confidence interval together, you can say that you are 95% sure that the true percentage of the population is between 43% and 51%. The wider the confidence interval you are willing to accept, the more certain you can be that the whole population answers would be within that range. For example, if you asked a sample of 1000 people in a city which brand of cola they preferred, and 60% said Brand A, you can be very certain that between 40 and 80% of all the people in the city actually do prefer that brand, but you cannot be so sure that between 59 and 61% of the people in the city prefer the brand. Factors that Affect Confidence Intervals
There are three factors that determine the size of the confidence interval for a given confidence level: Sample size
Percentage
Population size
Sample Size
The larger your sample size, the more sure you can be that their answers truly reflect the population. This indicates that for a given confidence level, the larger your sample size, the smaller your confidence interval. However, the relationship is not linear ( i.e., doubling the sample size does not halve the confidence interval).