Bias is an unwanted influence that favours a particular section of the population unfairly. Bias produces unreliable results because they are not truly representative of the population. Bias can come about because of
• a questionnaire with poorly written questions
• a sample that is not selected properly
Even when the information is researched correctly, the results can be misrepresented in
presentations or by the media in order to support a particular point of view. A good understanding of the statistical process will help you to interpret results properly.
0 Example 5
Andrew has written some questions to ask Club members about the club bistro.
a How often do you eat at our fabulous bistro?
b Rate your last meal: Great Yummy Quite nice
In what way are these questions biased? Rewrite them so that they are not biased.
a Using the word 'Fabulous' encourages the person answering the question to give a positive answer.
b This question doesn't give any negative
It would be better to ask: 'How often do you eat at the bistro?'
0 Example 6
Andrew is considering ways to find a sample of Club members to complete his survey. He thinks he could:
a ask 100 people as they come through the door on a Friday night b ask 100 people playing Bingo on a Wednesday morning.
In what way are these samples biased? How could you ensure that Andrew obtains a representative sample?
a Young members are more likely to be in the Club on a Friday night.
b People who are not working would be most likely to be in the Club on a Wednesday morning.
All age groups would not be represented fairly. Working members would be under
represented in the survey.
Andrew could obtain an alphabetical list of the members and choose every 100th member (other answers are possible).
Information that is collected can sometimes be presented poorly to favour a particular point of view.
0 Example 7
Alex stood at the school gate one morning and asked 10 students if they liked the school uniform. Five students said something negative about the uniform. Alex submitted a report to the school principal. In the report he stated that half the students hated the uniform. Explain three things that are wrong with this conclusion.
Alex only asks 10 students and it is not a random selection.
The question is vague and it's not clear what students don't like.
Alex exaggerates the answers when he says 'hate'.
32 I NELSON SENIOR MATHS Essentials 12
The sample is unlikely to be representative of ,
the student body.
It may not be the whole uniform that students don't like but possibly a particular item. We don't know how strongly students feel about the uniform.
Bias and misrepresentation
•§.iuHIIIn what way are these questions biased? Rewrite them so that they are not biased. a Do you prefer to holiday in fascinating Brisbane or wet Melbourne?
b Do you agree that we should increase the tax on those disgusting cigarettes? c Rate the last movie you saw: OK Good Fantastic
d Do you prefer exciting rugby league or boring old rugby union?
e Do you think that the Club is open long enough or should we be able to rage on into the early morning?
Rate your health fund: useless not much good reasonable
g Are there enough events for young people in this boring town?
h Isn't this just the greatest movie you've ever seen?
Are you one of those dumb people who walk to school? Rate the gym you attend: Best ever Good Ok
1§.iuHdIn what way are these samples biased? How could you ensure that an accurate sample is found?
a asking people their favourite sport in the crowd at an AFL match
b calling every sixth phone number on a page in the phone book to ask about mobile phone usage c surveying people about their preferred supermarket in a shopping centre with only one
d asking people in a major city for their view on drought support by the Government e asking teachers what music should be played at the Year 12 formal
surveying the Maths faculty on what is the best subject at school
g finding out what people think of a new design for a football club jersey by asking people who walk past the office door
h assessing voting intentions by asking people attending a Young Liberals conference who they will vote for in the next election
i§.j,jj.,UJane asks five of her fellow Year 12 students if they like the food at the school canteen. Three students say they don't like it. Jane writes an article for the school newspaper with the headline '60% of students hate canteen food'. Explain three things that are wrong with this headline.
4 A national company asks its customers via email to complete a survey about its service. It receives 25 replies, each of which makes some positive comments about the company's service. A report is completed for the CEO saying 'Customers 100% happy with our company'. Explain what is wrong with this summary.
5 A newspaper headline reads 'Disaster for Government program'. In the body of the article it is revealed that 5 out of 1000 students supported in their studies have failed. Explain why this headline is misleading.
6 Using the information you collected in the Investigation 'Travelling to school; write a presentation that is deliberately misleading. Perhaps you might like to write about additional student parking, motor bike parking, later school starting times or some other issue, but make sure you distort the true facts!
7 Use the Internet or the school library to find some newspaper or magazine articles that are based on statistics. Read them carefully and see if they have presented the information properly. Write a report on three of the articles you find, highlighting their use of statistics, either correctly or incorrectly.