Are opinion polls accurate?
                     Are opinion 
polls accurate?
Introduction
The accuracy or reliability of opinion polls is often 
questioned, especially when the polls are about voting 
intentions ahead of elections.
Source: www.markpack.org.uk
What is an opinion poll?
An opinion poll is a survey carried out to measure views 
on a certain topic within a specific group of people.
Source: africog.org
How are interviewees for an opinion poll 
selected?
The group of people interviewed for an opinion poll is called 
a sample. As the name suggests, a sample is a group of 
people that represents the total population whose opinion is 
being surveyed. In a scientific opinion poll, everyone has an 
equal chance of being interviewed.
Source: africog.org
How can such a small group be 
representative of the entire population?
In order to ensure that the sample/survey group is 
representative of the population, the surveyors must ensure 
that the group reflects the characteristics of the whole.
Source: africog.org
How are representative samples selected?
Random sampling involves unsystematically drawing the 
contact information of a certain number of people from a list 
of the relevant population, for example, a list of registered 
voters.
Source: africog.org
Are opinion polls accurate?
Well-designed polls are usually accurate within 3 percentage 
points. This level of accuracy of plus or minus about 3 
percent is referred to as the margin of error/sampling error. 
A well-designed poll is one which is representative of the 
population and contains balanced  questions which are not 
worded in a way to lead people to certain answers.
Source: africog.org
What is a margin of error/sampling error?
Since the sample does not include all the members of the 
population, statistics on the sample will generally differ from 
statistics on the entire population. 
A margin of error, also known as a sampling error, thus 
occurs due to the differences between statistical 
characteristics of a population and a sample drawn from 
that population.
Source: africog.org
Do sampling errors mean opinion polls are 
not accurate?
Polls are generally a good guide to the state of opinion, even 
in cases where the margin of error is larger than 3 percent. 
For instance, if a poll determines that a population is divided 
70% to 30% over an issue, a margin of error as big as 10% 
will not change the fact that one opinion is much more 
dominant than the other.
Source: africog.org
Thank you