1. Unit 3: Science of Psychology
WHS AP Psychology
Unit 3: Science of Psychology
Essential Task 3-6: Apply basic statistical concepts to explain research findings: - Descriptive Statistics: Central Tendency  (mean, median, mode, skewed distributions) Variance ( range, standard deviation, and normal distributions)
Logo Green is R=8 G=138 B= Blue is R= 0 G=110 B=184
Border Grey is R=74 G=69 B=64

2. The Science of Psychology
Approaches to Psych
Growth of Psych
Research Methods
Statistics
Descriptive
Correlation
Experiment
Case Study
Survey
Naturalistic Observation
Inferential
Ethics
Sampling
Central Tendency
Variance
Careers
We are here

3. Essential Task 3-6: Descriptive Statistics: Central Tendency Variance
Outline
Descriptive Statistics:
Central Tendency 
Mean, median, and mode
skewed distributions
Variance 
Range
standard deviation
normal distributions

4. Statistical Reasoning
Statistical procedures analyze and interpret data and let us see what the unaided eye misses.
OBJECTIVE 15| Explain the importance of statistical principles, and give an example of their use in daily life.
Composition of ethnicity in urban locales 4

5. Central Tendency
Tendency of scores to congregate around some middle variable
A measure of central tendency identifies what is average or typical in a data set 5

6. Measures of Central Tendency
Mode: The most frequently occurring score in a distribution.
Mean: The arithmetic average of scores in a distribution obtained by adding the scores and then dividing by their number.
Median: The middle score in a rank-ordered distribution.
OBJECTIVE 17| Describe three measures of central tendency and tell which is most affected by extreme scores. 6

7. But the mean doesn’t work in a skewed distribution
The Median is a much better measure of the center 7

8. Skewed distributions
Negatively Skewed
Positively Skewed 8

9. Measures of Variation
Statistical dispersion (how distributed the data points are) is a key concept in statistics.
Two key ways of measuring statistical dispersion
Range
Standard Deviation 9

10. Range
The range simply gives the lowest and highest values of a data set. 10

11. Standard Deviation Standard deviation gives a measure of dispersion.
Essentially, they are measures of the average difference between the values.
Standard deviation gives a value that is directly comparable to your mean values. 11

12. Formulas for Standard Deviation

13. Standard Deviation 13

14. Standard Deviation in Action
A couple needs to be within one standard deviation of each other in intelligence (10 points in either direction). —Neil Clark Warren, founder of eHarmony.com 14

15. Normal Distributions The distribution of data also gives us key info.
We know that many human attributes…
e.g height, weight, task skill, reaction time, anxiousness, personality characteristics, attitudes etc.
…follow a normal distribution. 15

16. Normal Distribution 16

17. IQ follows a Normal Distribution
Mean = 100
SD = 15 17

18. What percentage score below 100?
Mean = 100
SD = 15 18

19. What percentage score below 100?
Mean = 100
SD = 15 19

20. What percentage score above 100?
Mean = 100
SD = 15
34.1% % % 20

21. Normal Distribution 21

22. What percentage score between 85 and 100?
Mean = 100
SD = 15
34.1% 22

23. Normal Distribution 23

24. What percentage score between 85 and 115?
34.1% % = 68.2%
Mean = 100
SD = 15 24

25. What percentage score between 70 and 130?
Mean = 100
SD = 15
13.6% % % % = 95.4% 25

26. What percentage score below 70 and above 130?
Mean = 100
SD = 15 26

27. Interpret this graph
Figure 6. The distribution of IQ scores in male and female populations. Adjusted parameter values yielded a male-female gap of SD in g equivalent to 2.43 IQ points in favor of men 27