How to Obtain a Sample Size From a Huge Population

Obtaining an accurate analysis of a population is possible through sample polling and statistics. Polling every member of a large population would be prohibitively expensive and logistically difficult. Through mathematical analysis, it is possible to determine the accuracy, or margin for error, of the results from a given sample size when compared to the total population. Performing analysis of respective error margins from sample sizes guides the study.

Instructions

• 1

  Calculate the square root of a potential sample size for the survey. If the sample size is 2,500, the square root is 50.

• 2

  Divide 1 by the square root of the sample size. When 1 is divided by 50, the result is 0.02.

• 3

  Convert the number obtained by dividing 1 by the square root into a percentage. To obtain this figure, multiply by 100. When 0.02 is multiplied by 100, the result is 2, or 2 percent.

• 4

  Consider the the confidence interval in addition to margin of error. In a large population, the confidence interval is almost always 95 percent. You must also remember that every margin of error has a "confidence level," usually 95 percent. That means if you ask a poll question 100 times, 95 of those times the results would be within three percentage points of the original answer, according to nonpartisan research organization Public Agenda.

• 5

  Adjust the study according to the needs of the researchers. The sample size can be increased or decreased depending on the quality of information needed. Certain studies may require a lower margin of error to ensure factors such as human safety or quality of life.