Correlation and Distribution Flashcards
what are scatterplots used to display?
relations between two quantitative variables
positive relationship
both variables increase
negative relationship
variables change in opposite directions
strong relationship
points lie close to a line
weak relationship
points are widely scattered
perfect relationship
often appears when cheating has occurred, or when the same thing is being measured
what is the purpose of correlational analysis?
- determine whether there is a linear relationship between variables
- the direction and strength of relationships
pearson correlation coefficient
r
spearman correlation coefficient
rs
what do correlations make no distinction between?
the IV and DV
how can linear relationships be measured?
by correlations
correlations and non-linear relationships
correlations cannot be used, and data may need to be transformed
pearson correlation
- calculated directly from the raw score
- suitable for interval or ratio data
- highly affected by outliers
- not suitable for skewed data
spearman correlation
- calculated from the ranking of the raw scores
- suitable for ordinal data
- marginally affected by outliers
- suitable for skewed data
issues with sample size
small samples can indicate a pattern when there is no real relationship
when are density curves useful?
when dealing with lots of data, that can be distributed normally and generalised to the population
what do density curves use?
a mathematical model to describe a histogram distribution of scores
_______ and _______ ______ should be ignored
outliers, extreme values
normal distribution
perfectly skewed data
positively skewed data
right f
negatively skewed data
left f
what do density curves display?
the overall pattern of a distribution, as all the data is under the curve
when can predictions be made for distribution?
if certain values of the model are known, e.g., mean or SD
what can normal distributions be used to describe?
lots of naturally occuring data that is distributed similarly around a single measure of central tendency