5.4 Bias in Surveys
Statistical Bias – any factor that favours certain outcomes or responses therefore skewing the survey results.
Bias can invalidate the results of a survey.
Intentional bias can be used to manipulate statistics in favour of a certain point of view.
Unintentional bias can be introduced if the sampling and data-collection methods are not chosen carefully.
Leading and loaded questions contain language that can influence the respondents' answers.
Types of Bias
Sampling Bias – when the sample does not reflect the characteristics of the population. This can occur due to problems with either the sampling technique or the data-collection method.
Non-Response Bias – occurs when a particular groups are under-represented in a survey because they choose not to participate.
Measurement Bias – when the data-collection method consistently either under- or overestimates a characteristic of the population. Leading questions and loaded questions are examples of measurement bias.
Leading Question – a question that prompts a particular answer.
Loaded Question – a question containing information or language intended to influcence the respondents' answer.
Response Bias – when participants in a survey deliberately give false or misleading answers. The respondents might want to influence the results to be jerks or they might simply be embarrassed or afraid to answer honestly.
Ex 1 Identify the type of bias in the following situations.
(a) A highway engineer suggest that an economical way to survey traffic speeds on an expressway would be to have the police officers who patrol the highway record the speed of the traffic around them every half hour.
(b) A science class asks every fifth student entering the cafeteria to answer a survey on environmental issues. Less than half agree to complete the questionnaire. The completed questionnaires show that a high respondents are concerned about the environment and well-informed about environmental issues.
(c) A poll by a tabloid newspaper includes the question: “Do you favour the proposed bylaw in which the government will dictate whether you have the right to smoke in a restaurant?”
(d) A teacher has just explained a particularly difficult concept to her class and wants to check that all the students have grasped this concept. She asks her class who did not understand the concept.
(e) A survey asked students at a high-school football game whether a fund for extra-curricular activities should be used to buy new equipment for the football team or instruments for the school band.
(f) As part of a survey of the “Greatest Hits of All Time,” a radio station asks its listeners: Which was the best song by the Beatles?
(i) Help! (ii) Nowhere Man
(iii) In My Life (iv) Other:
(g) An aid agency in a developing country wants to know what proportion of households have at least one personal computer. One of the agency's staff members conducts a survey by calling households randomly selected from the telephone directory.
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