chapter 7

(not on slide) What 3 things affect the statistical significance of a correlation coefficient

1. Sample size 2. Magnitude of the correlation 3. How careful you want to be not to draw an inaccurate conclusion about whether the correlation is .00 (refers to type I and type II errors)

what is the most commonly used measure of correlation?

Pearson correlation (r)

true or false: correlation is the same things as causation

FALSE

List and describe the factors that could distort the correlation coefficient: (not on slide)

1. Restricted range - data in which participants' scores are confined to a narrow range of the possible scores on a measure. Having a restricted range artificially lowers correlations below what they would be if the full range of scores was present 2. An outlier is a score that is so obviously deviant from the remainder of the data that one can question whether it belongs in the data set. 3.Reliability of a Measure -- the less reliable a measure is, the lower its correlations with other measures will be.

what is the criteria for inferring causality? which of the three does correlational research satisfy (NOT on slide)

1.covariation- changes in one variable are associated with changes in the other variable 2.directionalilty- the presumed casual variable preceded the presumed effect in time 3.extraneous variables- all other variables that may affect the relationship between the two target variables are controlled/eliminated satifies 1, sometimes 2, NEVER 3

Describe the statistical significance of a correlation coefficient

A correlation coefficient is statistically significant when the correlation calculated on a sample has a very low probability of being .00 in the population from which the sample came. p<.05; less than 5% chance that the relationships is due to random chance WHAT DOES IT MEAN X may cause Y. OR Y may cause X. OR A third variable may cause X and Y. Spurious correlation - correlation between two variables due to their relation to other variables

Describe the direction of a correlation coefficient

Can be positive or negative when both variables increase or both decrease that is positive (direct); when one variable increases and the other decreases, this is a negative correlation (inverse)

What are the underlying assumptions of Pearson correlational analyses? Under what conditions do you use a pearson correlation?

Normal distribution Linearly related Continuous variables used with interval and ratio data

Define partial correlation

Partial correlation is the correlation between two variables with the influence of one of more other variables statistically removed. If a partial correlation between two variables (with the influence of a third variable removed) is significantly lower than the Pearson correlation between the two variables, then the correlation between them is at least partly due to the third variable (or to a variable associated with the third variable). example with kids tv hours/aggression/academic success

phi-coefficient correlational analyses?

Phi coefficient is used when both variables are dichotomous e.g. female/male and true/false

In what instances do you use other types of correlation coefficients: point biserial,

Point-biserial correlation is used when only one of the variables is dichotomous

Spearman rank-order

Spearman rank-order correlation is used when variables are measured on an ordinal scale (the numbers reflect the rank ordering of participants on some attribute)

describe the coefficient of determination (not on slide)

The correlation coefficient, r, is on a ratio scale so we can't add, subtract, multiply, or divide correlation coefficients or compare them directly. Therefore, we must square r to obtain the coefficient of determination. The coefficient of determination is on a ratio scale of measurement and is easily interpretable. Indicates the proportion of variance in one variable that is accounted for by another variable

what is a categorical variable

a variable that can take on one of a limited, and usually fixed, number of possible values, assigning each individual or other unit of observation to a particular group or nominal category on the basis of some qualitative property.

which is more commonly used in research: directional or nondirectional hypothesis ?

directional (predicts the direction of the correlation)

what is a continuous variable

infinite number of possible values e.g. time, weight

Describe the magnitude of a correlation coefficient

ranges from -1.00 to +1.00 .1= weak .3= moderate .5= strong when r=.00 there is no linear relationship between the two variable (no correlation) expresses the strength of the relationship between the two variables; unrelated to the sign (e.g. -.4 is stronger than a .01)

what is a correlation coefficient?

the statistics that indicates the degree to which two variables are related to one another in a linear fashion; shows magnitude and direction

what is a dichotomous variable

there are only two choices; ex: male v female, republican v democrat

What is correlational research used for

used to describe the relationship between two or more naturally occurring variables; examine to what extent do two variables covary (vary together)