Marketing Research Sample Size Calculator Essay Sample

Sample Size Calculator Footings: Confidence Interval & A ; Confidence Level The assurance interval ( besides called border of mistake ) is the plus-or-minus figure normally reported in newspaper or telecasting sentiment canvass consequences. For illustration. if you use a assurance interval of 4 and 47 % per centum of your sample picks an reply you can be “sure” that if you had asked the inquiry of the full relevant population between 43 % ( 47-4 ) and 51 % ( 47+4 ) would hold picked that reply. The assurance degree Tells you how certain you can be. It is expressed as a per centum and represents how frequently the true per centum of the population who would pick an reply lies within the assurance interval. The 95 % assurance degree means you can be 95 % certain ; the 99 % assurance degree means you can be 99 % certain.

Most research workers use the 95 % assurance degree. When you put the assurance degree and the assurance interval together. you can state that you are 95 % sure that the true per centum of the population is between 43 % and 51 % . The wider the assurance interval you are willing to accept. the more certain you can be that the whole population replies would be within that scope. For illustration. if you asked a sample of 1000 people in a metropolis which trade name of Cola they preferred. and 60 % said Brand A. you can be really certain that between 40 and 80 % of all the people in the metropolis really do prefer that trade name. but you can non be so certain that between 59 and 61 % of the people in the metropolis prefer the trade name. Factors that Affect Confidence Intervals

There are three factors that determine the size of the assurance interval for a given assurance degree:
* Sample size
* Percentage
* Population size

Sample Size
The larger your sample size. the more certain you can be that their replies genuinely reflect the population. This indicates that for a given assurance degree. the larger your sample size. the smaller your assurance interval. However. the relationship is non additive ( i. e. . duplicating the sample size does non halve the assurance interval ) . Percentage

Your truth besides depends on the per centum of your sample that picks a peculiar reply. If 99 % of your sample said “Yes” and 1 % said “No. ” the opportunities of mistake are distant. irrespective of sample size. However. if the per centums are 51 % and 49 % the opportunities of mistake are much greater. It is easier to be certain of extreme replies than of centrist 1s. When finding the sample size needed for a given degree of truth you must utilize the worst instance per centum ( 50 % ) . You should besides utilize this per centum if you want to find a general degree of truth for a sample you already have. To find the assurance interval for a specific answer your sample has given. you can utilize the per centum picking that reply and acquire a smaller interval. Population Size

How many people are at that place in the group your sample represents? This may be the figure of people in a metropolis you are analyzing. the figure of people who buy new autos. etc. Often you may non cognize the exact population size. This is non a job. The mathematics of chance proves the size of the population is irrelevant unless the size of the sample exceeds a few per centum of the entire population you are analyzing. This means that a sample of 500 people is every bit utile in analyzing the sentiments of a province of 15. 000. 000 as it would a metropolis of 100. 000. For this ground. The Survey System ignores the population size when it is “large” or unknown.

Population size is merely likely to be a factor when you work with a comparatively little and known group of people ( e. g. . the members of an association ) . The assurance interval computations assume you have a echt random sample of the relevant population. If your sample is non truly random. you can non trust on the intervals. Non-random samples normally result from some defect in the sampling process. An illustration of such a defect is to merely name people during the twenty-four hours and lose about everyone who works. For most intents. the non-working population can non be assumed to accurately stand for the full ( working and non-working ) population. hypertext transfer protocol: //www. surveysystem. com/sscalc. htm # one