1. Data Gathering Techniques
Samples and Surveys

2. 2 Types of Data
1. Numerical
2. Categorical

3. Numerical examples include things like how many, height, weight,
salary,
etc

4. Categorical examples include things like what kind, what type,
what color,
etc
ask for specific examples, ie sports, movies, eyes, hair...

5. Population
all members of a set

6. Sample Part of a Population
If you determine a sample carefully, the statistics for the sample can be used to make general conclusions about the larger population.

7. Sampling Types Methods used to select samples Convenience
Self-selected
Systematic
Random

8. Convenience Sample
select any members of the population who are conveniently and readily available
define different sample types by the methods used to select them

9. Self-selected sample
select only members of the population who volunteer for the sample

10. Systematic sample
order the population in some way, like alphabetically, and then select from it at regular intervals

11. Random sample
all members of the population are equally likely to be chosen

12. Bias A systematic error introduced by the sampling method.
A sample has a bias when a part of a population is
overrepresented or underrepresented

13. Identify the sampling method. Determine if there is any bias.
A newspaper wants to find out what percent of the city population favors a property tax to raise money for local parks.
A newspaper article on the tax increase invites readers to express their opinions on the newspaper’s website.
self-selected; bias depends on who visits website

14. Identify the sampling method. Determine if there is any bias.
A newspaper wants to find out what percent of the city population favors a property tax to raise money for local parks.
A reporter interviews people leaving the city’s largest park.
convenience; bias overrepresents park supporters

15. Identify the sampling method. Determine if there is any bias.
A newspaper wants to find out what percent of the city population favors a property tax to raise money for local parks.
A survey service calls every 50th listing from the local phone book.
systmatic, bias if there is some link btw people listed & people who pay property tax

16. Identify the sampling method. Determine if there is any bias.
The students planning the junior class party want to know what kinds of pizza to buy. They ask the pizza restaurant what kinds sell the most.
convenience, restaurant sells to other people besides students (underrep.)

17. Study Methods
another way to collect sample information is to perform a study
observational
controlled
survey

18. Observational study
measure or observe members of a sample in such a way that they are not affected by the study
ask for examples of things that are studied, ie. student behavior, shoppers, etc

19. Controlled experiment
Divide the sample into 2 groups.
Impose treatment on one group but not on the other “control” group
Then compare the effect on the treated group to the control group.

20. Survey
Ask every member
of the sample
a set of questions

21. analyzing study methods
Which type of study method is described in each situation?
Researchers randomly choose two groups from 10 volunteers. Over a period of 8 weeks, one group eats ice cream before going to sleep, and the other does not. Volunteers wear monitoring devices while sleeping, and researchers record dream activity.
Should the sample statistics be used to make a general conclusion about the population?
controlled experiment. stats are based on small sample, findings unreliable for general conclusion

22. analyzing study methods
Which type of study method is described in each situation?
Students in a science class record the height of bean plants as they grow.
Should the sample statistics be used to make a general conclusion about the population?
observational study. may make conclusions, however soil type, amt of sunlight, water, fertilizer and other factors my affect the growth

23. analyzing study methods
Which type of study method is described in each situation?
Student council members ask every 10th student in the lunch line if they like the cafeteria food.
Should the sample statistics be used to make a general conclusion about the population?
survey. (convenient systematic) results not reliable b/c people in like are more likely to enjoy cafe food than those who brought lunch from home. WHAT TYPE OF SURVEY IS MORE LIKELY TO YIELD BETTER RESULTS?

24. analyzing study methods
Which type of study method is described in each situation?
A pharmaceutical company asks for volunteers to test a new drug to treat high blood pressure. Half the volunteers will be given the drug, and half will be given a placebo. The researcher will monitor the blood pressure of each volunteer.
Should the sample statistics be used to make a general conclusion about the effectiveness of the drug in the larger population?
controlled study, reliable, if other factors are random like age, gender, and overall health

25. Designing a survey
SPORTS During the 2008 Olympic Games, a U.S. swimmer won more medals than any other swimmer in history.
What sampling method could you use to find the percent of students in your school who recognize that swimmer from a photograph.
systematic, every nth entering school (usually least amt of bias)

26. survey question
SPORTS During the 2008 Olympic Games, a U.S. swimmer won more medals than any other swimmer in history.
What is an example of a survey question that is likely to yield information that has no bias?
“Who is pictured in this photograph?” if photo does NOT contain things like swimming pool or medals or Olympic symbol

27. ADDITIONAL PROBLEMS GIVE TYPE OF SAMPLING METHOD
DOES THE SAMPLE HAVE A BIAS?

28. Politics
A political candidate wants to know what percent of his constituency favors a Referendum A on an upcoming ballot election.
His staff asks each person who comes into the candidate’s office for 3 days whether they support Referendum A.
convenience, may share candidate’s opinions more than population as a whole

29. Management
The manager of a grocery store wants to determine what percent of shoppers use store coupons.
He asks every 10th shopper who passes through the store’s door for the next week if he or she intends to use a store coupon on his or her visit.
systematic, no bais

30. study method? use stats?
Scientists study the effects of the phases of the moon on the levels of low tide and high tide in 200 coastal cities in the U.S. for a period of 12 months.
observation, reliable since several locations used and data collected over long period of time

31. study method? use stats?
A pet food company randomly chooses two groups of 20 puppies for a study. One group eats a new brand of dog food and the other group eats an off-brand of dog food for a period of 4 weeks. Researchers record muscular and skeletal growth rates in both groups.
controlled, unreliable b/c small sample and type of puppies

32. study method? use stats?
For a class project, students in Health class ask every tenth student entering the school if they eat breakfast in the morning.
survey, systematic. reliable b/c random students selected

33. NCFE type question
To determine the most popular brands of tea consumed by Americans, a survey is conducted in a busy downtown location at lunch time.
Which of the following is NOT a potential bias in the sampling method?

34. least biased
Urban office employees are not representative of the general population.
The results could be influenced by national brand teas available in the area.
A lunchtime survey does not reflect peoples’ tastes at other times of the day.
The survey must include call-in and online responses. d

35. Take note of samples and surveys used in different places.
math is everywhere