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2.4 BIAS IN SURVEYS

2.4 BIAS IN SURVEYS. The results of using a sample to make predictions or inferences about a population are only accurate if the sample is representative of the population. The methods for choosing the sample and collecting (measuring) the data must be free from BIAS. 2.4 BIAS IN SURVEYS.

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2.4 BIAS IN SURVEYS

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  1. 2.4 BIAS IN SURVEYS • The results of using a sample to make predictions or inferences about a population are only accurate if the sample is representative of the population. • The methods for choosing the sample and collecting (measuring) the data must be free from BIAS

  2. 2.4 BIAS IN SURVEYS • STATISTICAL BIAS is any factor that favours certain outcomes or responses which systematically skews the survey results • A BIASED SAMPLE is a statistical sample in which members of the population are not equally likely to be chosen

  3. 2.4 BIAS IN SURVEYS • SAMPLING BIAS • Sampling bias occurs when the sampling frame does not reflect the characteristics of the population • Sampling Frame – the group of individuals that actually have a chance of being selected from the population

  4. 2.4 BIAS IN SURVEYS Example – SAMPLING BIAS An ad agency in a developing country wants to know what proportion of households have at least one computer. The survey was conducted by randomly selecting households from the telephone directory • There could be a significant number of households without telephones • May over-estimate the proportion of households with computers • A better way would be to visit randomly selected homes, however, it may be more expensive.

  5. 2.4 BIAS IN SURVEYS NON-RESPONSE BIAS • Occurs when particular groups are under-represented in a survey because they choose not to participate • A voluntary response sampling technique can lead to Non-Response Bias • People least interested in the issue will tend not to respond to a a survey

  6. 2.4 BIAS IN SURVEYS MEASUREMENT BIAS - When the data collection method consistently over or underestimates the characteristic of the population MEASUREMENT BIAS – Leading Question When suggested answers to questions are listed in the question • Example – What is your favourite video game? a) Mario Striker b) Tetris c) ESPN NHL 2K10 d) other

  7. 2.4 BIAS IN SURVEYS MEASUREMENT BIAS – Loaded Questions • When questions are asked in such a way as to influence the way the respondent will answer • Example – “Not having MP3 players in class will reduce the number of distractions to students in the class. Are you in favour of raising the achievement levels of students by banning MP3 players from the school?”

  8. 2.4 BIAS IN SURVEYS RESPONSE BIAS • When participants in a survey deliberately give false or misleading answers • Respondents may want to influence the outcome of the survey results or they may be afraid to answer the question truthfully out of embarrassment or sensitivity • Example – Teachers asks “Who has ever cheated on a test?”

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