1. Science of Psychology AP Psychology
Essential Task: 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
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3. Essential Task: 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. 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. Negatively Skewed (aka left-skewed or long left tail)
Skewed Distributions
Negatively Skewed (aka left-skewed or long left tail)
Positively Skewed
In a negatively skewed distribution, the mean is usually less than the median because the few low scores tend to shift the mean to the left. In a positively skewed distribution, the mode is always less than the mean and median 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 (the extent to which values of a variable differ from a fixed value such as the mean)
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. Steps to compute Standard Deviation:
1. Find the mean of the data set (total scores ÷n).
2. Compute the distance from each data point from the mean (plus or minus does not matter).
3. Square each of your scores from step 2.
4. Add the all the points form 3.
5. Divide by your n (number of data points in your set).
6. Take the square root.

13. Formulas for Standard Deviation

14. Standard Deviation 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