Psy exam 3

If the correlation between variables is .70, what percent of the following variance is shared (i.e. the coefficient of determination) ?

(70)2 70 x 70 = 49 49%

Indirect Correlation

(the negative one) means that variables change in the opposite direction

Direct Correlation

(the positive one) means that the variables change in the same direction (both go up or both go down)

The coefficient of determination is:

- Is more precise than looking at the correlation coefficient - the percentage of variance in one variable that is accounted for by the variance in another - Is a measure of shared variance

Computing A Simple Correlation Coefficient

- rxy= is the correlation coefficient (outcome - our goal) of X and Y - n= is the sample size - ∑= is the "Sum of" sign - X= is the individual's score on the X variable - Y= is the individual's score on the Y variable - XY= is the product of each X score times its comparable Y value - X2= is the individual's X score, squared - Y2= is the individual's Y score, squared

Which of the following has the weakest correlation? A) -.90 B) 0.50 C) -.15 D) 0.78

-.15

If the correlation coefficient is -.25, what % variance is shared ?

-.25 x -.25 = .0625 6.25%

What is stronger, a +.52 correlation or a -.58 correlation?

-.58

A correlation can range from __ to __

-1 to 1

Which of these is the weakest correlation?

.01 because it's closest to 0

Which is not a possible correlation between exam scores and GPA? A) -0.10 B) 0.90 C) 0.25 D) 1.25

1.25

If the correlation between variables is .70, what percent of the variance is not shared variance (the coefficient of non-determination / alienation)?

100 - 49 = 51 51%

If the highest exam score is a 20 and the range is 5, what's the lowest score?

15

If the variance is 9, the standard deviation is ___

3

If the variance for a dataset is 49, what is the standard deviation?

7

What is the range for the data set below? 2, 5, 7, 1, 9, 4, 4, 8, 6, 1

8

Interpreting a Correlation Coefficient

8 to 1.0 (+ or -) Very Strong Relationship .6 to .8 (+ or -) Strong Relationship .4 to .6 (+ or -) Moderate Relationship .2 to .4 (+ or -) Weak Relationship .0 to .2 (+ or -) Weak or No Relationship

Correlation coefficient

A numerical index that reflects the relationship between two variables

Which of the following correlations would be interpreted as a weak relationship? A) -.26 B) -.46 C) -.66 D) -.86

A) -.26

If the coefficient of determination is .25, what is the Pearson correlation coefficient? A) 0.50 B) -.25 C) .25% D) 2.5

A) 0.50

We found a correlation of .99 between hours of studying and exam scores, what does this mean? A) Studying causes high exam scores B) There's a positive relation between studying and exam scores C) There's a negative relation between studying and exam scores D) High scores causes studying

B) There's a positive relation between studying and exam scores

In research studies, we want _____ group variability to be high and _____ group variability to be low

Between: Within

A correlation between two variables is called

Bivariate correlation

If the variance is 4 what is the standard deviation ? A) 1 B) 3 C) 2 D) 4

C) 2

The lower your exam scores, the greater amount of tears your instructor sheds. A) Example of positive correlation B) Example of curvilinear correlation C) Example of negative correlation D) None of the above

C) Example of negative correlation

The range is: A) A subtraction of the lowest score from the highest score B) The least informative measure of spread C) Sensitive to outliers D) All of the above

D) All of the above

A ___ correlation means the variables involved change in the same direction

Direct

A ____ correlation means the variables change in the same direction (both go up, or both go down)

Direct and Positive

In a normal curve, the ____ is in the center of the curve

Mean, Median and Mode

A correlation of -.19 is most likely _____ and _____

Negative; weak or no relationship

A correlation of .88 is most likely _____ and _____

Positive; strong

Which of the following is one way to represent the Standard deviation ?

S

The standard deviation is calculated by:

Taking the square root of the variance

rxy represents:

The correlation coefficient

Variability

The extent to which the scores in a data set tend to vary from each other and from the mean.

The closer a correlation is to -1 or +1, the stronger it is

Thus a .70 is stronger than a .45, but a -.77 is stronger than a .70

Which statement is true regarding variability?

Variability between conditions related to the IV is good

S2 is the symbol for ___

Variance

Computing The Variance

Where: S2 = The variance (our goal in figuring out this formula!) ∑ = The Greek "sum of" sign. X = Each individual score __ X = The mean of all of the scores. n = The sample size

Bivariate Correlation

a correlation between two variables, hence the "bi" phrase

A correlation close to -1 is a weak correlation

false

A correlation of zero between two variables means the variables are ___

not related

Variance

refers to a single number that represents the total amount of variation in a distribution

If the coefficient of determination between two variables is.81, what is the Pearson correlation coefficient ?

square root .81 = .90 .90

Standard Deviation

the square root of the variance

The standard deviation is very sensitive to outliers

true