1. Chapter 17 Uses and Abuses of Statistics

2. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Survey A bus company conducts a passenger opinion survey to improve the quality of its services. Librarians conduct a survey on borrowed books to understand the most popular type of books with readers.

3. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Before running a retail shop, investors conduct a market research to assist in finding out the most suitable location for the shop. Survey

4. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Census The Census and Statistics Department of Hong Kong carries out a population census every ten years to provide valuable and reliable information for the Hong Kong government and other organizations. website: http://www.info.gov.hk/censtatdhttp://www.info.gov.hk/censtatd

5. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Population and Sample Population Sample

6. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Sample Survey A survey which takes only a sample of data is called a sample survey. For example, a bus company collected opinions from 300 passengers in a survey.

7. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Sampling Methods A good sampling method should ensure every individual in the population has a chance to be selected.  Simple random sampling  Systematic random sampling  Stratified random sampling  Convenience sampling

8. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Simple Random Sampling In simple random sampling, each datum from a population is to be selected at random to form a sample.

9. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Systematic Random Sampling In systematic random sampling, all data in a population are organized as a sequence, and every n data are grouped together. Then a datum, e.g. the kth datum (where 1  k  n) is selected randomly from the first group and all of the remaining groups, i.e. the kth, (k  n)th, (k  2n)th etc of the sequence, are selected to form a sample.

10. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Stratified Random Sampling In stratified random sampling, a population is divided into some strata or groups, and then a sample in a specific size is selected randomly from each stratum.

11. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Convenience Sampling In convenience sampling, a sample is selected conveniently from a part of the whole population. Therefore, convenience sampling does not involve a random selection of data from the whole population.

12. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Data Collection Methods  Observation  Questioning

13. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Design of Questionnaires  Questions are relevant to the objective of the survey.  Questions are clear enough to avoid misunderstanding and misinterpretation.  Questions are neutral, free from misleading elements and carefully worded to avoid leading interviewees to a desired answer. A good questionnaire should have the following elements.

14. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Design of Questionnaires  Questions are easy to understand and avoid using unnecessary technical terms.  Questions take care of interviewee’s emotion so as to avoid causing embarrassment, uneasy or unpleasant feeling. A good questionnaire should have the following elements.  The questionnaire is short and precise.

15. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Procedure of A Survey

16. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Market research Uses of Statistics Activity planning

17. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Abuses of Statistics  Misinterpretation of statistical findings A labour union released a report of a survey in September 2002. One of the main findings was as follows: ‘An estimated 20 percent of all families have family member(s) not being employed.’ Based on the above statement, a magazine wrote a headline ‘One in five families suffers from unemployment.’

18. 2005 Chung Tai Educational Press © Chapter Examples Quit Chapter 17 Uses and Abuses of Statistics Abuses of Statistics  Biased sampling At the end of a health TV programme, the audience was asked to express their opinions by phone about the prohibition of smoking in all restaurants. They could press 1 to vote for or 2 to vote against the idea after the line is connected. After a 4-hour survey, there were 268 out of 300 votes for and 32 against the idea. It was then announced that 90% of the public support the prohibition of smoking in all restaurants.

19. End