Polls will often present candidates running for election as winning or losing ba
ID: 3065029 • Letter: P
Question
Polls will often present candidates running for election as winning or losing based on the results of recent surveys. When presenting the poll, there is usually information about a “margin of error.” What does that mean?
For example, consider that one survey, conducted by a professional polling organization, shows Candidate Q with 49% with a plus or minus margin of error of 2 percentage points (usually depicted as ±2%). The same survey shows the other candidate, Candidate Z having an estimated 47% of likely voters and the same margin for error (±2%).
However, consider that another survey taken of the same population in the same day by a different professional polling organization has different results. In this survey, Candidate Z has polled at 49% while Candidate Q, has only polled at 46%. This survey has a 3-percentage-point margin of error (±3%).
Review the textbook pages on the topic of confidence intervals for proportions. Consider the assumptions you would have to make to be able to compare the information given in these polls and explain the differences. Then take your best guess as to who may be ahead in the race
Explanation / Answer
The margin of error is the range of values below and above the sample statistic in a confidence interval. The confidence interval is a way to show what the uncertainty is with a certain statistic (i.e. from a poll or survey).
The margin of error is a statistic expressing the amount of random sampling error in a survey's results. The larger the margin of error, the less confidence one should have that the poll's reported results are close to the "true" figures; that is, the figures for the whole population. Margin of error is positive whenever a population is incompletely sampled and the outcome measure has positive variance (that is, it varies).