Correlation

What is a positive correlation?

association between two variables. The variables tend to have similar scores with respect to their mean and spread.

What is psychometrics?

branch of statistics used in the development of tests and measures.

Is a correlation of -0.35 weaker than that of a correlation of 0.10?

No, the sign does not indicate strength

What are the steps for finding the denominator for the pearson correlation?

1. calculate a sum of squares for each variable 2. multiply the two sums of squares 3. take the square root of the product of the sums of squares.

What are the three main characteristics of a correlation coefficient?

1. can be either positive or negative 2. falls between -1.00 and 1.00 3. It is the strength and not the sign that indicate how large it is.

What are the limitations of Correlation?

1. correlation does not mean causation 2. restricted ranges 3. effect of an outlier

What are three possible casual explanations for a correlation?

1. first variable might cause the second variable 2. the second variable might cause the first 3. a third variable may have an effect on both the first and the second variables.

What are the steps for finding the numerator for the pearson correlation?

1. for each score calculate the deviation from its mean 2. for each participant we multiply the deviations for his or her two scores 3. we sum the products of the deviations

What are the assumptions for a correlation coefficient?

1. randomly selected 2. normal distribution 3. each variable should vary equally, no matter the magnitude of the other variable.

TRUE OR FALSE. A is worth talking about when it has a correlation coefficient of 0.50.

False. It is rare that there are correlations with such a strong correlation coefficient.

What is reliability?

Measure that is consistent

What is a valid measure?

One that measure what it was intended to measure

Why is it important to start off with constructing a scatter plot before initiating a correlation coefficient calculation?

See whether there is linearity and to sense the direction and strength of the relation between the two variables.

What is one type of reliability?

Test-retest reliability which refers to where the scale being used provides consistent info every time the test is taken.

TRUE OR FALSE. The scores in a negative correlation move up and down in opposition to each other, like a teeter-totter.

True

TRUE OR FALSE. The scores in a positive correlation move up and down together, the same way the mercury rises in a thermometer as the temperature goes up.

True

TRUE OR FALSE. A correlation of 0.00 falls right in the middle of two extremes and indicates no correlation--no association between the two variables.

True.

TRUE OR FALSE. The correlation coefficient can be used as a descriptive and inferential statistic.

True. Descriptive to descriptive the direction and strength of an association.

TRUE OR FALSE. If we calculate a correlation coefficient that is outside the range of -1.00 and 1.00, then we've made a mistake in our calculation.

True. Values MUST fall between the range of -1.00 and 1.00

What is one thing we must ask ourselves about range when thinking about correlation coefficient?

Whether the ranges of the two variables are sufficient enough to show us their true association.

The number that we calculate when we quantify a correlation is __________

a coefficient

What is a correlation coefficient?

a statistic that quantifies a relation between two variables

What is a negative correlation?

an association between two variables with variables such as one having a high score and the other having a low score.

What is correlation?

association (or relation) between two variables; co-relation.

How do we calculate the degrees of freedom?

dfr= N-2

A correlation of 1.00 indicates a perfect________correlation, while a correlation of -1.00 indicates a perfect______correlation.

positive; negative

What is the comparison distribution for the pearson correlation?

r distribution

What are Cohen's guidelines to the strength of a correlation?

small: 0.10, medium: 0.30, large: 0.50

What is the Pearson correlation coefficient?

statistic that quantifies a linear relationship between two scale variables. Its symbol is "r".

What is partial correlation?

technique that quantifies the degree of association between two variables after statistically removing the association of a third variable with both of those variables.

What does partial correlation control?

the effect of a third variable.

What is one straightforward way to determine whether an individual falls above or below the mean?

to calculate deviations for each score.

How many times is the test given to the sample in a test-retest reliability?

twice; typically with a delay of a week or more between tests

Correlation studies usually measure relations between...

two scale (interval or ratio) variables

In regards to the pearson correlation, what are we trying to test using the hypothesis testing?

whether a correlation is statistically significantly different from no correlation--an r of 0.