![]() Multiplying a probability value by 100 converts it into a more intuitively accessible percentage measure. Non-significant = fairly likely to have occurred through mere chance. While any value larger than 0.05 is regarded as Significant = fairly unlikely to have occurred through mere chance, By the conventional canons of statistical inference, a probability value equal to or less than 0.05 is regarded as ![]() The bottom line in such a test is a probability value, ranging between 0.0 and 1.0, which represents the likelihood that a difference between (1) and (2) as great as the one observed might have occurred through mere chance. The result one would expect to find, on average, if nothing other than mere chance coincidence, mere random variability, were operating in the situation. In this event, the analysis is performed on the subset of respondents who did express preference for either X or Y and the result must accordingly be referred to the subset of the general population of voters who at at the time of the poll would have had a preference for either X or Y.Īll tests of statistical significance involve a comparison between In some polls the percentages for X and Y do not add up to 100%, because some number of respondents express preference for a candidate other than X or Y, or for no candidate at all. The 50/50 split that would be expected if there were no difference between the percentages of preference for the candidates within the general population. The split (e.g., 52/48, 46/54) between the reported percentages for the two major candidates, X and Y, and Poll I Poll II X I = % X II = % n I = n II = Difference = % z = ±Ĭalculator 4: Significance of the Difference between the Results for Candidate X and Candidate Y in a Single Pollįor any particular poll, this calculator will assess the significance of the difference between The percentage reported for Candidate X in poll II The percentage reported for Candidate X in poll I It is a modified version of the VassarStats calculator for "The Significance of the Difference between Two Independent Proportions." The values you need to enter before clicking the "Calculate" button are This calculator will assess the significance of the difference between these two percentages. Suppose there are two separate polls, I and II, in which Candidate X gets 43% and 48%, respectively. (Recall that margin of error is inversely related to sample size.)Ĭalculator 3: Significance of the Difference between the Results of Two Separate Polls For example, with a reported margin of error of ± 4%, the lower and upper limits will be calculated using 4.49 and 3.51, respectively. If the reported margin of error is entered as an integer, the programming for Calculator 2 will assume it to be a rounded value and calculate the lower and upper limits of estimated sample size based on the reported margin of error ± 0.49 percentage points. In cases if this sort, Calculator 2 will estimate the size of the sample on the basis of two items of information that probably will be given in the report: the margin of error and the largest of the candidate percentages. It occasionally happens that the press report of a poll will give no indication of the size of the sample on which the poll is based. These upper and lower limits are precisely equidistant from theĮstimated population percentage only when that percentage isĬalculator 2: Estimating Sample Size when the Report of a Poll Fails to Provide that Essential Bit of Information The 'margin of error' reported here is calculated as one-half theĭistance between the upper limit and the lower limit. They also often appear to be based on the percentage for the candidate who has the majority or plurality within the sample. Note: For polls reported in the news media, the margins of error tend to be rounded to the nearest integer. This calculator will also work if the sample percentage for only one of the candidates is entered. Enter the respective percentages of respondents within the sample who favor Candidate X and Candidate Y into the top two cells enter the size of the sample into the third cell and then click the "Calculate" button. This calculator can be used for analyzing the results of a poll of your own (in which case, keep in mind the requirement of a representative sample) or for checking the preciseness of the results of polls reported in the news media. Significance of the Difference between the Results for Candidate X and Candidate Y in a Single PollĬalculator 1: Estimated Population Percentage and Margin of Error Significance of the Difference between the Results of Two Separate Polls Estimated Population Percentage and Margin of ErrorĮstimating Sample Size when the Report of a Poll Fails to Provide that Essential Bit of Information
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