Transcript Choosing the Appropriate Statistics

Choosing the
Appropriate
Statistics
Dr. Erin Devers
October 17, 2012
Quantitative or Qualitative?
 Is
the data quantitative or qualitative?
 If qualitative, you have to do the hard
work of coding the material numerically
before analyzing it.
Level of Measurement?
 Nominal


Descriptive stats: mode
Inferential stats: chi-square
 Ordinal

Descriptive stats: median
 Interval/Ratio


Descriptive stats: mean and standard
deviation
Inferential stats: it depends
Chi-Square (ϰ2)
 Indicates
whether a distribution of
frequencies is what you would expect
 If distribution is significantly different from
what is expected, then it suggests there is
a true difference present
 Examples
Example: Are more males or
females diagnosed with
schizophrenia?
Male
50
Female
50
Guys
Girls
70
30
* p < .001
Interval/Ratio Data: Did you
conduct an experiment?
 Correlation
and Regression
 t-test, ANOVA
Correlation Joke
Correlation Coefficient:
 Definition:
number that represents the
relationship between two variables.
 Answers
the question, how are changes in X
related to changes in Y?
 Gives
you information regarding

Strength of the relationship

Direction of the relationship
Linear Regression
Basic premise: given previous
observations, one can (within some range
of error) predict what is likely to occur in
future
Examples:
 GRE scores and performance in grad school
 Parental smoking and smoking in teens
 Cholesterol level and risk for heart attack.
 Maternal depression and childhood
psychopathology
 Workers level of responsibility and job
satisfaction
 Beliefs and what one will do within a certain
situation.
t-tests
 Provide
a way to compare two group
means with each other
 Paired or Independent (depends on
whether you used a between or within
subjects design)
ANOVA: Analysis of Variance
F
statistic
 Takes into account the fact that chances
of getting a difference randomly goes up
with multiple comparisons.
 F = t2
 Comparing means of multiple groups
e.g. What dose of a drug works best for
arresting hallucinations in schizophrenia?
Questions?