# Sample Size Calculation

Autor: rita • September 21, 2011 • Essay • 310 Words (2 Pages) • 951 Views

**Page 1 of 2**

There are two steps for us to calculate the sample size:

Calculate the confidence interval

Confidential interval is a margin of error reflection, which can give an estimation range of value which includes the unknown parameter. Highest per cent confidence level means that the data will be reality which can be 99%, 95% or 90%.

x ̅±z*(σ/√n)

Use confidential interval to calculate sample size

n=(■(Z_(x/z)&σ)/E)^2

The confidence interval (also called margin of error) is the plus-or-minus figure usually reported in newspaper or television opinion poll results. For example, if you use a confidence interval of 4 and 47% percent of your sample picks an answer you can be "sure" that if you had asked the question of the entire relevant population between 43% (47-4) and 51% (47+4) would have picked that answer.

The confidence level tells you how sure you can be. It is expressed as a percentage and represents how often the true percentage of the population who would pick an answer lies within the confidence interval. 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

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