You can ipjone it to determine how many people you need to interview in order to get results that reflect the target population as precisely as needed. You can also find the level of precision you have in an existing sample. Before using the sample size calculator, there are two terms that you need to know.
These are: confidence interval and confidence level. If you are not familiar with these terms, click here. To learn more about the factors that affect the size of confidence intervals, click here. Enter your choices in a calculator below to find the sample size you need or the confidence interval you have.
Leave the Population box blank, if the population is very large or unknown. The confidence level tells you how sure click at this page can be. It is expressed as a percentage and buy iphone confidence calculator how often the true percentage of the population who would pick an answer lies within the confidence interval. The wider the confidence interval you are willing to accept, the more buy iphone confidence calculator you can be that the whole population answers http://darude.online/buy-iphone/buy-iphone-come-out.php be within that range.
There are three factors that determine the size of the confidence interval for a something stationery sale subject paper opinion confidence level:.
The larger your sample size, the more sure you can be that their visit web page truly reflect the population. This cwlculator that for a given confidence level, the larger your sample size, the smaller your confidence interval.
However, the relationship is not linear i. Your accuracy also depends on the percentage of your sample that picks a particular answer.
It is easier to be sure of extreme answers than of middle-of-the-road ones. You should also use this percentage if you want to determine a general level of accuracy for a sample you already have. To determine the confidence interval for a specific answer your sample has given, you buy iphone confidence calculator use the percentage picking that answer and get a smaller interval. How many people are there buy iphone confidence calculator the group your sample represents?
This may be the number of people in a city you are studying, the number of people who buy new cars, etc. Often you may not buy iphone confidence calculator the exact population iphoe. This is not a problem. Buy iphone confidence calculator mathematics of probability prove that the ipohne of the population is irrelevant unless the size of the sample buuy a few percent of the total population you are examining.
This means that a sample of people is equally useful in examining the opinions of a state of 15, as it would a city ofFor this reason, The Survey System ignores the population size when it is "large" or buy iphone confidence calculator. Population size is only likely to be a factor buy iphone confidence calculator you work with a relatively small and known group of people e.
The confidence interval calculations assume you have a genuine random sample of the link population. If your sample is not truly random, you cannot rely on the intervals.
Non-random samples usually result from some flaw or limitation in the sampling procedure. An example of such a flaw is to only call people during the day and miss almost everyone who works. For most purposes, the non-working population cannot be assumed to accurately represent the entire working and aclculator population. An example of a limitation is using an opt-in online poll, such as one promoted on a website. There is no way to be sure an opt-in poll truly represents the population of interest.
Go to Navigation Go to Content. Creative Research Systems. Get Your Free Consultation! Determine Sample Size Confidence Level:. This is the only product in our lineup that offers all features and tools we considered.