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Tank - Our Lives in Numbers September 8, 2016 5 key things to know about the margin of error in election polls By Andrew Mercer8 comments In presidential elections, even the smallest changes in horse-race poll results seem to become imbued margin of error excel with deep meaning. But they are often overstated. Pollsters disclose a margin of error margin of error calculator sample size so that consumers can have an understanding of how much precision they can reasonably expect. But cool-headed reporting on polls is margin of error calculator ti 84 harder than it looks, because some of the better-known statistical rules of thumb that a smart consumer might think apply are more nuanced than they seem. In other words, as is so often true in http://wolfweb.unr.edu/homepage/scavote/MarginofErrorCal.htm life, it’s complicated. Here are some tips on how to think about a poll’s margin of error and what it means for the different kinds of things we often try to learn from survey data. 1What is the margin of error anyway? Because surveys only talk to a sample of the population, we know that the result probably won’t exactly match the “true” result that we would get if we interviewed http://www.pewresearch.org/fact-tank/2016/09/08/understanding-the-margin-of-error-in-election-polls/ everyone in the population. The margin of sampling error describes how close we can reasonably expect a survey result to fall relative to the true population value. A margin of error of plus or minus 3 percentage points at the 95% confidence level means that if we fielded the same survey 100 times, we would expect the result to be within 3 percentage points of the true population value 95 of those times. The margin of error that pollsters customarily report describes the amount of variability we can expect around an individual candidate’s level of support. For example, in the accompanying graphic, a hypothetical Poll A shows the Republican candidate with 48% support. A plus or minus 3 percentage point margin of error would mean that 48% Republican support is within the range of what we would expect if the true level of support in the full population lies somewhere 3 points in either direction – i.e., between 45% and 51%. 2How do I know if a candidate’s lead is ‘outside the margin of error’? News reports about polling will often say that a candidate’s lead is “outside the margin of error” to indicate that a candidate’s lead is greater than what we would expect from sampling error, o
the reliability of ACS estimates. Adding the MOE to the estimate provides an upper limit and subtracting the MOE from the estimate provides a lower limit of the range where the true value of the estimate most likely actually falls. http://www.datacenterresearch.org/data-resources/neighborhood-data/margin-of-error/ How do I write about margin of error (MOE) in a grant report? Here are some examples of how you can write about this data in a grant report: “From 2010 to 2014, somewhere between 59.1% and 59.9% of people http://www.aapor.org/Education-Resources/Election-Polling-Resources/Margin-of-Sampling-Error-Credibility-Interval.aspx commuted less than 30 minutes to work.” “From 2010 to 2014, at least 20% (or no more than 30%) of people in a neighborhood live below the poverty line.” “From 2010 to 2014 the Census estimates that 30.6% of margin of people traveled between 30 and 60 minutes, although this percentage could range from 30.3% to 30.9%.” Making comparisons taking into account the margin of error (MOE) The margin of error (MOE) makes it tricky to compare different places or timeframes. For instance, it is hard to tell if a poverty rate of 10% (+/–2%) is really higher than a poverty rate of 7% (+/– 2%) even though the two estimates are different. The widget below will do a calculation for margin of error you and let you know if the two estimates are statistically different. You can impress your funders, by telling them whether the difference between the two data points is “statistically significant.” Test Statistical Significance 1. Enter the percents (%) or dollar amounts ($) that you want to compare and the margin of error (MOE) for each. Important: Only include numbers. Include a zero before the decimal point for numbers less than one. Do not include a comma, or $, % or +/-. Percents (%) or dollar amounts ($): Margins of error (MOEs): 2. 3. Is the difference "statistically significant at the 90% confidence interval"? 4. Be sure to write down your results on a piece of paper. How do I write about “statistical significance” in a grant report? Here are some examples of how you can write about statistical significance in a grant report: “From 2010 to 2014 the poverty rate in area X was between X% and X% which is significantly higher than the poverty rate for Orleans Parish at the 90% confidence interval.” “From 2010 to 2014, X% of residents had less than a 9th grade level, which is significantly higher than in 2000 at the 90% confidence interval.” Source: American Community Survey (ACS) Guide. Metropolitan Area Planning Council. Retrieved May 17, 2012 from http://www.mapc.org/sites/default/files/MAPC-Guide-to-American-Community%20Survey.pdf Note: For technical users, note that the Census 2000 Summary
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