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Mean
interval
Mean Formula
Median
Ordinal
Compute Median
List the values in order
Mode
Nominal
How to Compute the Mode
List all the values in a distribution but list each value only once
Nominal measurement
defined by the characteristics of an outcome that fit into one and only one class or category.
Ordinal Measurement
stands for order
Interval measurement
test or an assessment tool is based on some underlying continuum such that we can talk about how much more a higher performance is than a lesser one.
Ratio level of measurement
characterized by the presence of an absolute zero on the scale.
A measure of central tendency for qualitative
categorical
The median and the mean are best used
with Quantitative data
A correlation coefficient
a single number
Computing a simple correlation coefficient
Linear correlation
relation between two variables that shows up on a scatter diagram as the dots roughly following a straight line
Eyeball Method
Perhaps the easiest (but not the most informative) way to interpret the value of a correlation coefficient is by eyeballing it and using the information
The coefficient of determination
r^2
Coefficient of alienation
the amount of variance in one variable that is not accounted for by the variance in another variable
Correlations Limitations
Outliers
Correlation Matrix
a table showing a simple way to report all relevant correlations at once
Reverse causation
the causal direction could be the opposite from what has been hypothesized
Reciprocal Causation
two variables cause each other
Common Causation
x and y are affected by a third variable
Variability
the spread or dispersion of data
Range
most basic measure of variability
Range Issues
Ignores values in the middle
Interquartile Range (IQR)
Q3 - Q1
Standard deviation
reflects how much scores differ from one another
Standard deviation formula
Steps: 1. List each score. It doesn't matter whether the scores are in any particular order
Always report mean and SD together
High SD means
values farther from the mean on average
Low SD means
the data point is close to the mean!
Variance
standard deviation squared
Standard deviation is susceptible to outliers
outliers are two SD from the mean
X-bar ± (c * s)
c = cutoff scores
Where to start with Good Graphs
Frequency distribution
A frequency distribution is
a method of tallying and representing how often certain scores occur
Class Intervals
typically 2
Histogram
a visual representation of the frequency distribution where the frequencies are represented by bars
Density Plots
smoothed histograms
Frequency polygon
shape tracking frequencies
Skew direction
the tail always tells you the direction of the skew. Negative
Kurtosis
the "peakedness" of the distribution
Histograms are for what variables
continuous
Bar Charts are for what variables
categorical
Scatterplots show
the relationship between two quantitative variables on the same individual
Reliability
consistency
Classical Test Theory
observed score = true score + error
Test-retest reliability
used when you want to examine whether a test is reliable over time
Parallel Forms
used when you want to examine the equivalence or similarity between two different forms of the same test
Inter-rater reliability
measure of how much independent raters agree on ratings
Internal consistency reliability
The more pr
Note 
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