Bias can occur in statistics in many diff erent ways. For example, bias exists where: ● ●


the sample is not representative the sample size is too small


● ●


all members of the population don’t have an equal chance of being selected for a sample the question is leading or confusing, e.g. ‘Don’t you agree that …?’


Discuss and discover


Working with a classmate: (i) Design a questionnaire to fi nd out information about the students in your class.


(ii) What method will you use to collect the data? (iii) Classify all data collected. (iv) What conclusions can you draw from the data you collected?


(v) If you were to do this again, what could you improve? (Was your question fair or did it introduce bias? Was the data collected relevant?)


Practice questions 18.2


1. Each of the following questions can be improved. Write a more statistically correct question and explain why you think it is better. (i) Do you spend a lot of time doing homework? (ii) Do you usually walk to school or ride your bike? (iii) Do you prefer to watch mindless comedies or exciting dramas? (iv) Don’t you think the price of a cinema ticket is too high? (v) Do you like fruits and vegetables? (vi) Do you agree that we need at least 8 hours sleep a night?


(vii) Do you think students should be allowed to use spell check because it automatically improves spelling?


(viii) What is the best football team in the Premier League?


2. For each question below, choose an appropriate method of data collection to investigate the question. Explain your choice.


(i) What are the fi ve largest (by population) cities in Ireland? (ii) What are the favourite bands of the students in your class? (iii) How many times does the average person blink per minute? (iv) How many red cars are in the car park?


3. The principal of a school visited each class in his school and asked for a show of hands to fi nd out how many students had ever been bullied at school. Only two students raised their hands.


(i) Do you think this is a good method to collect data? Justify your answer.


(ii) What do you think the principal would conclude from his results? Do you think his conclusion would be accurate?


(iii) Can you suggest a better way to fi nd out how many students have been bullied? 288 Linking Thinking 1


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