1. The Four Techniques for Gathering Data
September 2, 2011

2. The Four Techniques OBSERVATIONAL STUDY SAMPLE SURVEY CENSUS
EXPERIMENT

3. Observational Study
You observe, but do not interact, so you do not influence the responses of who/what you are observing.
The purpose of an observational study is to draw conclusions about some group or situation.

4. Observational Study
You may not know what to write down at first. You may need to write down everything before you see patterns forming.

5. What makes this an example
of an observational study?

6. Sample Survey
Sample surveys are a type of observational study, as the person conducting the study does not provide anything which could influence the results.
Sample surveys ask questions of only some of the population.
A population in a study is the entire group of individuals for which we want information.

7. Sample Survey
A sample is part of a population from which we actually collect the data, which is then used to draw conclusions about the population.
A sample is used when it is not practical to gain information about the entire population.

8. The CPS is the most important government sample survey in the U. S
The CPS is the most important government sample survey in the U.S. Many variables concern the employment status of everyone over the age of 16. It also records many other economic and social variables. The population is more than 100 million households; the sample size is 50,000 households per month.

9. Census
A sample survey that attempts to include the entire population in the sample.
U.S. Censuses are administered every 10 years in order to determine if political boundaries need to be adjusted (block-by-block population figures are needed to create election districts with equal populations). This is the most important reason.

10. Census
Previously, there were long forms and short forms. Long forms were sent to 1/6 of the households with more detailed questions. However, starting with 2010, everyone completed a 10 question short form questionnaire.
Censuses do not have to be only this type; any sample survey that includes the whole population is a census (this could include all students of a school, all residents of a city, etc.)

11. Census
What do you think could happen with a census to produce inaccurate results???
College students living away from
home may be counted twice, and the homeless may not be counted at all.

12. What makes a sample survey different from a census?
Question…
What makes a sample survey different from a census?

13. Experiments
Experiments impose some treatment on some of the people in a group, a different treatment (placebo) to the people in another group, then compare.

14. Experiments
A treatment can be some new type of medication to be tested which needs evidence of success/safety to be made available to the public.

15. Experiments
The experimenter judges whether there is a response (until the end of the experiment, the experimenter does not know who received the treatment and who received the placebo).

16. Question…
Why do you think it is important that the experimenter does not know who received the treatment and who received the placebo?

17. Homework Assignment #1
Look through newspapers, magazines, and the Internet. Bring in multiple examples of observational studies, sample surveys, census, and experiments that have been done. Try to find at least one of each type. If you can find more than one of any type, bring it in. We will be comparing the differences between each type of data gathering technique and need many examples.
Due on Wednesday, September 7.