2.4 BIAS IN SURVEYS

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# 2.4 BIAS IN SURVEYS - PowerPoint PPT Presentation

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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Presentation Transcript
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
• 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

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

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.

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

2.4 BIAS IN SURVEYS

MEASUREMENT BIAS - When the data collection method consistently over or underestimates the characteristic of the population

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

2.4 BIAS IN SURVEYS