Calculation of the sample |
Description of the calculator: In the input field «Total population size», enter the whole nonnegative number equal to the number of objects in the population which is sampling. For example, it may be amount of documents in the array or, more often, the number of inhabitants living in a particular area, or the number of people in the target group. In practice, we can observe situations when the sample is 100 or more times smaller than the population. In this case, the population is considered to be quasiinfinite. This is the default setting (symbol «∞» in the «Total population size»). Then you need to select the level of probability that will define the sampling error or its size by clicking the left «mouse» button on the right circle. The higher the probability the lower the chance that the actual error will be beyond the scope of theoretical estimate or the calculated size of sample will be not sufficient to make estimates with an accuracy of no more than a given error. If we set the probability as P, the probability that the estimate of the error or the size will be incorrect equal to 1-Р. When P=0,95 probability of error is 0,05 (1 chance in 20); with P=0,99 the same probability is equal to 0,01 (1 chance in a 100). If you want to calculate the sampling error of a certain amount, then the «Sample size» enter a non-negative number equal to the number of objects in the sample. After that, with left «mouse» button click you will do a calculation, which must became green after correct entering the input data. In «Theoretical statistical error» will be displayed the number greater than 0 and less than one, in which is used instead of a comma dot «.» (up to 3 digits after the decimal point). If you want to translate this error into a percentage, simply multiply the number by 100 – and visualize moving the decimal point two digits to the right. Thus, in the example the calculation results show that the theoretical error of probability random sampling with population size 1600 with quasiinfinite population with probability 0,99 less than 0,032 (3,2%).
In case, when you need to calculate the size of a sample with kvazineskinchennoi population sufficient to provide a theoretical statistical error is no greater than a given, you have to fill in the «Theoretical statistical error» (a number from 0 to 1, instead of a comma «,» – dot «.»; percentages must be translated into the proportion of units: 3,2%=0,032 etc.). You must also specify the probability by clicking the left «mouse» button on the right circle in the to the right of the «Probability». After that, you just need to click the left mouse button on the green button «Calculate» and the «Size of sample» you will see the result. To enter new data and re-calculate, press the black button «Reset». |