1. Quiz 1 Version 1 Version 2 Version 3 1. D A C 2. 3. B 4. 5. 6. 7. 8.9.
10.

2. The Construction of Knowledge
Building Reality
The Construction of Knowledge

3. Issues of Validity and Reliability
Validity: Accurateness, i.e., is the measure/instrument used actually measuring what the researchers want it to measure?
Reliability: Repeatability, i.e., if another researcher repeated the study with the same method and a different representative sample from the same population, would they get the same results?

4. But is it Reliable?

5. Who Would You Vote For?

6. But are they Symmetrical?

7. Real Life Example

8. The Problem of Averages
What information are we seeking when we ask for the average ?

9. The Standard Normal Distribution
= Mean, Median, and Mode

10. An Illustration
Averages (means) are highly sensitive to extreme values.
Example:
$40,000
$50,000
$80,000
$30,000
$20,000

11. Calculating Measures of Central Tendency
Mean:
=($20,000 + $30,000 + $40,000 + $50,000 + $80,000) / 5
= $44,000
Median
$20,000 $30,000 $40,000 $50,000 $80,000
But…what if one person gets their dream job…

12. $500,000
$50,000
Mean:
=($20,000 + $30,000 + $40,000 + $500,000+ $80,000) / 5
= $134,000
Median
$20,000 $30,000 $40,000 $80,000 $500,000

13. Mode
Median ($50,233)
Mean ($67,609)
Number of Individuals
Income

14. Correlation and Causation

15. Determining Causation is Difficult
Must explain away alternative causes
Example: Gateway Drugs
Marijuana Use
Use of Harder Drugs
Association with Hard Drug Users

16. Determining Causation is Difficult
Must explain away alternative causes
Example: Gateway Drugs
Marijuana Use
Use of Harder Drugs
Peer Pressure

17. Interpreting Sampling Error
As of September 23, 2008:
Gallup Polls show
44%
47%
± 2% sampling error

18. Interpreting Sampling Error
Sampling error is the variation you could expect from taking multiple random/representative samples
If we want to generalize to the population of voters we must consider sampling error as follows:
Between 45% and 49% of voters support Obama (47 ± 2)
Between 42% and 46% of voters support McCain (44 ± 2)
It is impossible to determine a leader with this data!

19. So…When Faced with Information…
Is the sample representative of the population?
Are the measures used valid and reliable?
Have the correct statistical methods been applied and have they been interpreted correctly?
Did they cite the mean when they should have used the median?
Did they jump from correlation to causation?
Was sampling error correctly interpreted?