1. Correlational Research
Detects relationships between variables.
Does NOT say that one variable causes another.
There is a positive correlation between ice cream and shark attacks. Does that mean that ice cream causes shark attacks?

2. Measured using a correlation coefficient.
A statistical measure of the extent to which two factors relate to one another

3. How to Read a Correlation Coefficient

4. Which of the following has the strongest relationship?.5
-.5
-.98
-.75
.75
.005

5. Create a Scatterplot with the data: Relatively Strong Negative
Number of doors a car has
Average Driving Speed 2 3 4 5 6 7 8 73 75 60 55 50 48 45
What kind of correlation exists?
Relatively Strong Negative

6. Scatterplots
Perfect positive
correlation (+1.00)
Scatterplot is a graph comprised of points that are generated by values of two variables. The slope of the points depicts the direction, while the amount of scatter depicts the strength of the relationship.

7. Correlational Research
Correlation is the relationship between two variables.
Positive correlation – both values increase
Negative correlation –
One variable increases, while the other decreases.
Correlational Coefficient – strength of the relationship
0= no relationship
+1 or – 1 = perfect relationship
Examples: SAT scores and success in college; Red wine and heart attacks; Prejudice and age; length of marriage and hair loss, etc.

8. Scatterplots Perfect negative No relationship (0.00)
correlation (-1.00)
No relationship (0.00)
The Scatterplot on the left shows a negative correlation, while the one on the right shows no relationship between the two variables.

9. There is a moderate positive correlation of +0.63.
Scatterplot
The Scatterplot below shows the relationship between height and temperament in people.
There is a moderate positive correlation of

10. Disconfirming evidence
Illusory Correlation
The perception of a relationship where no relationship actually exists. Parents conceive children after adoption.
Confirming evidence
Disconfirming evidence
Do not
adopt
Adopt
Do not conceive
Conceive
OBJECTIVE 10| Describe how people form illusory correlations.
Michael Newman Jr./ Photo Edit

11. Confounding Variables
Length of a marriage has a positive correlation with hair loss in men.
Does marriage cause hair loss?
Do balding men make better husbands?
Does another factor underline this correlation?

12. Correlation and Causation
OBJECTIVE 9| Explain why correlational research fails to provide evidence of cause-effect relationships.

13. Which of the following would prove his prediction?.5
-.05
.80
-.68
.51
.005

14. Think of a confounding variable
+ Correlation btw. Men with nice cars and wealth.
Conclusion: having a nice car makes you wealthy
+ Correlation btw. wearing bifocals and cancer.
Conclusion: wearing bifocals may lead to cancer
- Correlation btw. hours spent at the tutoring center and scores on college exams.
Conclusion: Studying is bad for exam scores

15. Disconfirming evidence
Illusory Correlation
The perception of a relationship where no relationship actually exists. Parents conceive children after adoption.
Confirming evidence
Disconfirming evidence
Do not
adopt
Adopt
Do not conceive
Conceive
OBJECTIVE 10| Describe how people form illusory correlations.
Michael Newman Jr./ Photo Edit

16. Coach Z thinks there is a relationship between the average height of his girls varsity basketball team and the number of wins they have each season.
What kind of correlation does he believe exists?
What are two things coach Z could do to investigate this relationship?

17. Correlation between avg. height of a girls basketball team and wins21 18 15
Wins 12 9 6 3 65 67 69 71 73
Avg. Height

18. Which of the following is this probably a scatterplot for?
A) GPA and days at School
B) Height and Weight
C) Self Esteem and Depressive Moods
D) Weight and Reading Level

19. STATS
The average person has one ovary and one testicle!

20. Measures of Central Tendency
Single score that represents a whole set of scores
Mode
Mean
Median

21. Mode Simplest Most frequently occurring score in a data set
40, 67, 67, 72, 72, 76, 83, 83, 83, 88, 93, 98
What is the Mode? 83

22. When the Mode does not tell the whole story
Midterm Scores:
55, 55, 81, 85, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 100
How does the mode misrepresent our data?

23. Mean Most reported measure of central tendency
The average of a data set
Total sum of all of the scores/divided by the number of scores
Mean is most accurate when there is least variation (range).

24. Good/Bad Tips for the night 10, 5, 10, 20, 5 Mean = 10 Income
100,000, 60,000, 75,000, 80,000, 8,000,000.
Mean = 1,663,000

25. Skewness
One or a few extremely low scores pull the mean below the median.
One or a few extremely high scores pull the mean below the median.

26. A Skewed Distribution
Are the results positively or negatively skewed?

27. Median The midpoint or 50th percentile
Arrange all data from highest to lowest
Find Center- Average if given an even number of data sets
Incomes:
84, 000, 100,000, 60, 000, 75, 000, 80, 000, 8, 000,000.

28. Seven members of a boys' club reported the following individual earnings from their sale of cookies: $2, $9, $8, $10, $4, $9, and $7. In this distribution of individual earnings?
the median is greater than the mean and greater than the mode.
the median is less than the mean and less than the mode.
the median is greater than the mean and less than the mode.
the median is less than the mean and greater than the mode.
the median is equal to the mean and equal to the mode.

29. Range and Standard Deviation
Measures of Variation
Range and Standard Deviation

30. Range- the gap between the lowest and highest scores
Measures of Variation
Range- the gap between the lowest and highest scores

31. The standard deviation is kind of the "mean of the mean," and often can help you find the story behind the data. Tells you how likely the scores will look like the mean.

32. ? M:4 SD: 1.6 M:3.5 SD: 1.6 M: 7.1 SD: .5 M: 2.5 SD:.5 M:5.1 SD: 1.2

33. Standard Deviation
Which of the following data sets would have the highest and lowest standard deviation?
15, 16, 12, 14, 15, 17
.25, 1.5, .5, 1.5, .5
7, 20, 4, 20, 0, 5
1, 500, 42, 0, 0, 150

34. Agenda Hand in PsychSim (please put in folder)
Statistical Significance
What is it? why is it important?
The Normal Curve and Standard Deviation
Where do we see it? How do we use it?
Stats Practice
Partner practice for quiz.
HW:
PsychSim: Desc. Stats
PsychPort 3
Quiz tomorrow Module 3

35. Statistical Significance
A result that is not likely to occur randomly, (by chance) but rather is likely to be attributable to a specific cause is statistically significant.
Can be strong or weak
Strong= the results are probably not due to chance (sampling error)
Weak= the results might be due to chance.
The level at which one can accept whether an event is statistically significant is known as the significance level or p-value.

36. Standard Deviation- whether scores are packed together or dispersed
When the scores are tightly clustered the standard deviation is small.
When the scores are spread apart there is a relatively large standard deviation.

37. Variance Another way to look at the variability of the data
To get the variance: square the standard deviation.
So if the standard deviation is 5 the variance is ?.

38. Standard Deviation
To understand this concept, it can help to learn about what statisticians call normal distribution of data.
mean = median = mode
symmetry around the center
50% of values less than the mean and 50% greater than the mean
Many things closely follow a Normal Distribution:
Heights of people
SAT test scores
Infant weights
size of things produced by machines
IQ scores
blood pressure
Shoe size

39. But let me show you graphically what a standard deviation represents...
13.6%
34.1%
34.1%
13.6%
2.15%
2.15%
Mean

40. One standard deviation (the red area on the above graph) accounts for around 68 percent of the people in this group. Two standard deviations away from the mean (the red and green areas) roughly 95 percent of the people. Three standard deviations (the red, green and blue areas) account for about 99 percent of the people.

41. Percentiles

42. But let me show you graphically what a standard deviation represents...
13.6%
34.1%
34.1%
13.6%
2.15%
2.15%
Mean

43. Question 1
IQ scores have a mean of 100 and a standard deviation of 15, what percentage of people would score above 85?
84%
27%
75%
94%
99%

44. Practice Question 2: In a normal distribution of intelligence test scores with a mean of 100 and a standard deviation of 15 what percentage of people would score above 115? 95 68 16 84 98

45. In a normal distribution of intelligence test scores with a mean of 100 and a standard deviation of 15 what percentage would be closest to people that would score below 85? 95 68 16 84 97

46. Q3: In a normal distribution of height in men with a mean of 70 inches and a standard deviation of 2 inches. If Devin is in the 98 percentile, which of the following is closest to his height?
6’0”
6’6”
5’8”
6’2”
5’10”

47. 64 66 68 70 72 74 76

48. Practice Question 3
Amy’s SAT score is in the 99th percentile. (Remember SAT scores have a mean of 1100 and a standard deviation of Of the following, which score is closest to this?
A) 950
B) 1100
C) 1580
D) 1400
E) 1260

49. 34.1%
34.1%
13.6%
13.6%
2.15%
2.15%
.2%
.2%
620
780
940
1100
1260
1420
1580

50. Computing Compute the mean for the data set.
Compute the deviation by subtracting the mean from each value.
Square each individual deviation.
Add up the squared deviations.
Divide by one less than the sample size.
Take the square root.

51. HOW TO?
The standard deviation is a measure of how spread out your data are. Computation of the standard deviation is a bit tedious. The steps are:
Compute the mean for the data set.
Compute the deviation by subtracting the mean from each value.
Square each individual deviation.
Add up the squared deviations.
Divide by one less than the sample size.
Take the square root.

52. Question 1
In a normal distribution of scores with a mean of 82 and a standard deviation of 7, what percentage of people would score above 75?
84%
27%
75%
98%
99%

53. 34.1%
34.1%
13.6%
13.6%
2.15%
2.15%
.2%
.2% 55 70 85
100
115
130
145

54. But let me show you graphically what a standard deviation represents...
13.6%
34.1%
34.1%
13.6%
2.15%
2.15%
Mean

55. 34.1%
34.1%
13.6%
13.6%
2.15%
2.15%
.2%
.2% 64 66 68 70 72 74 76

56. 34.1%
34.1%
13.6%
13.6%
2.15%
2.15%
.2%
.2%
620
780
940
1100
1260
1420
1580

57. Practice Questions
Amy’s SAT score is in the 99th percentile. (Remember SAT scores have a mean of 1100 and a standard deviation of Of the following, which score is closest to this?
A) 950
B) 1100
C) 1580
D) 1400
E) 1260