“What do I need to do?” Cheat Sheet: Becki Paynich IACA 2013
Statistic/Measure/Test
Mode
Clues
Most freq-can be used for all levels (nominal
and ordinal most useful)
Median
Middle Score-can be used for ordinal ranges,
usually only used for interval level
Mean
Average—Can be used for ordinal, but
strongly advised only for interval. Sensitive to
outliers. When you have outliers, also use the
median (or only use median)
Range
Difference between lowest and highest score.
Variance
Sum of Squares divided by N
Standard Deviation
Square root of the variance. Used only on
interval level data. How disperse or spread out
(or tall or flat) your distribution is. A normal
distribution is when the mean and the median
are the same number.
Formula
Percentile. What proportion (or %) people had
more ___ than your case. What proportion (or
%) people had less___ than your case.
2 formulas.
Estimate what the population (mean or
proportion) would be….given a sample mean
and standard deviation or proportion.
Measures of Central Tendency
(Descriptive Statistics)
Measures of Dispersion
Z (Individual case)—standardizes your data.
Confidence Intervals
*Pu = .5
One Sample Z (or T) tests
2 formulas.
Test whether or not a sample (mean or
proportion) is significantly different (or higher
or lower) than a population.
*Pu = is given to you in the problem or in
another data source.
Two Sample Z (or T) tests
2 formulas (2 or more steps)
Test whether or not a sample (mean or
proportion) is significantly different (or higher
or lower) than another sample (mean or
proportion). (Usually comparing 2 groups)
ANOVA
One-way (SST, SSB, SSW)…
Compare the means of 3 or more
samples/groups. Test whether or not there is
a significant difference across 3 or more
groups/samples.
Chi-Square
Non-parametric. Does not assume a normal
distribution.
Are variables dependent/independent of one
another? Do groups differ on any given
measure? Only for nominal and ordinal. Only
want 5x5 table at the MOST. The smaller the
table, the more reliable chi-square is.
Expected frequencies must be 5 or greater in
80% of the cells. If not, need to use Yates
correction on chi-square.
Nominal
Lambda
Ordinal
GAMMA, Kendall’s (most common) or
Spearman’s Rho
Measures of Association
See Handout “Interpretation Guide” for
details.
Measures of Association Cont.
Interval
Pearson’s R, Spearman’s Rho (use if skewed
data)
All the ordinal and interval MOAs above.
Used to look at how a third variable (gender,
race, religion, etc.) impacts the measure of
association. If the partial correlation
coefficient is significantly different than the
correlation coefficient for the whole sample,
than your third variable impacts it.
Partial Coefficient
Can be bivariate (only one X) or multivariate.
Regression
See Handout “Interpretation Guide” for
details.
Different formulas for different levels of
measurement of the dependent variable (Y).
Usually only use linear regression for interval
level dependent variables.
Values interpreted the same as MOAs above.
Several key pieces of information to examine
(See other handout) including, R2, model
significance, standardized beta coefficients,
unstandardized beta coefficients, and
significance levels of beta coefficients.