Home > Flashcards > Print Preview
The flashcards below were created by user
Anonymous
on FreezingBlue Flashcards. What would you like to do?

What is correlation?
correlation
measures the relationship between two variables
there are more than one type of correlation (depending on level of measurement)

Pearson product moment correlation
correlation
between interval/ratio variables
most widely used measure of correlation
has the most assumptions

Speraman rank correlation
correlation
between ordinal variables

Phi coefficient
correlation
between dichotomous variables

pointbiserial correlation
correlation
between a dichotomous & interval/ration variables
ex: right or wrong of an exam item and total score

biserial correlation
correlation
between a dichotomous (w/ underlying continuum) & interval/ratio variables
ex:anxiety (low, high) & depression

polyserial correlation
correlation
between a polytomous (3 or more levels) (w/ underlying continuum) & interval/ratio variables
ex: anxiety (low, medium, high) & depression

tetrachoric correlation
correlation
betwee dichotomous variables (w/ underlying continuum) and depression
ex: anxiety (low, high) & depression (low, high)

polychoric correlation
correlation
between polytomous variable (w/ underlying continuum)

Pearson Product Moment Correlation Assumptions
correlation
No Outliers
Linearity
Normal Distribution

Pearson Assumptions: No Outliers
correlation
no extreme scores
 two types:
 univariate
 multivariate

Pearson Assumption: No Outliers  Univariate
correlation
an extreme score that is far away from the distribution of a variable
only one variable

Pearson Assumption: No Outliers  Multivariate
correlation
an extreme score that is far away from the joint distribution of variables
it is possible for a case to be a multivariate outlier without bieng a univaritate outlier

Pearson Assumption: Linearity
correlation
variables should NOT show any nonlinear pattern

Pearson Assumption: Normal Distribution
correlation
distribution of a variable should be univariate normal
distribution of variables should be multivariate normal

Range of Correlation
correlation
 all correlation range from 1 to +1
 a measure of correlation is unitless (or standardized).
 r = 1 perfect negative relationship
 r = +1 perfect positive relationship
 r = 0 no relationship

Scatterplot
correlation
when the correlation is r= +1, the scatterplot appears in a straight line
as the correlation approaches 0, the variability of scores increases

Covariance
correlation
measures of relationship between two variables in raw units (unstandardized correlation)
possible range is infinity to +infinity

Types of Research Questions
correlation
1. Is there a significant relationship between x and y?
2. Is there a significant difference in the relationship of x and y between group 1 and group 2?
3. What is the (1alpha)%CI of the correlation?

Sampling Distribution Correlation
correlation
 in not normal except when r=0 due to restricted range of the correlation
 bound between 1 & +1

Onesample ttest for correlation
correlation
For testing H_{0}: p = 0, Greek letter rho  population correltaion
df = N  2
affected not only by N but also by r. Depends on the # of subjects & relationship

When to us rcritical
correlation
when testing more than one correlation becomes tedious
easier to compute rcritical value as long as there are same N

Fisher's rtoz transformation
when to use
correlation
For testing a H_{0}: p = p_{0}_{ }
For difference in a correlation between groups
For confidence interval of a correlation
Convert r to zscore

