Do you ever wonder how margins of error in political opinion polls are so precise? For example this article on the race for the Republican nomination for this year’s presidential election in the US describes how a national telephone poll had a margin of error of +/-4%.
The answer lies in the number of people who expressed their opinion. In this case that number was 600. The people who designed the poll chose that “600” deliberately. They chose it because they wanted a margin of error of +/-4%. If they had been after more accuracy and wanted a tighter margin of error, for example, +/-3%, they would have chosen a higher number of respondents. Researchers make these choices based on a number of factors. One such factor could be cost. The more people who take part in a poll – the more accurate the poll’s results. But it costs money to get people to answer questions!
If you have any questions on the above, feel free to contact me.