Statistical Methods Flashcards 1
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| range | length of the smallest interval which contains all the data
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| interquartile range (IQR) | difference between the third and first quartiles
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| Variance | amount of variation of all the scores for a variable s(square)=sum (x-mean(x))(square)/N
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| Standard Deviation | square root of variance
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| Normal Distribution | two-thirds of cases within one standard deviation of the mean
two-thirds of cases within one standard deviation of the mean
approximately 95% of cases within two standard deviations of the mean
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| Deviation | x-x(mean)
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| Experimental research design | a scientific control is used to minimize the unintended influence of other variables
Random assignment of subjects
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| Quasi-experimental design | Experimental method but without random assignment
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| When is quasi experimental design used? | when randomization is impossible and/or impractical
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| Advantages of quasi experimental design | Easier
minimizes threats to external validity
efficient in longitudinal research
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| Disadvantages of quasi experimental design | Threats to internal validity
Causal relationships difficult to determine
Confounding variables
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| Internal validity | extent to
we can accurately state that the
independent variable produced the observed
effect
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| Threats to internal validity | regression to the mean
confounding variables
extraneous variable occurring between pre- and post-measurement
maturation
instrumentation error
investigator bias
differential attrition
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| External validity | Generalizability
– to or across target populations
– to or across tasks
– to or across environments
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| Threats to external validity | situation or environment
Hawthorne effect (testing effect)
Rosenthal effect
Selection bias
pre and post test effects
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| Hawthorne effect | People act differently when they know they are being tested
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| Non-experimental design | No control group
Observational
Used for theory development
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| cross tabulation | A table of the frequency distribution of two or more variables
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| Null hypothesis | hypothesis of no difference
Something happens by chance or that no difference exists between populations
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| Chi-square (χ2) | compares a set of frequencies expected if the null hypothesis is true (fe) against a set of frequencies observed in a sample (fo)
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| Geometric mean | used for data based on ratios, proportionate growth, percentage change.
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| differential attrition | extent of subjects who drop out of a study
AKA mortality
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| reliability | consistency of observations
not the same as validity (could be consistently false)
reliability is necessary BEFORE validity can be established
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| Social desirability effect | Subject respond in a way that appears favorable to the tester
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| Advantages of interviews | higher response rate
more lengthy and detailed
more complex
more flexible
linking
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| Advantages of questionnaires | low cost
protectivity (confidential)
less reactivity
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| reactivity | act of measuring changes responses
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| Cohort study | Compare group of people who share a certain characteristic (smokers) with unexposed group(non-smokers).
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| Experimental trial | Exposed v. unexposed groups in trial setting (drug v. placebo)
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| Case control study | Historical,
Subjects already have a condition, study looks back to see if there are characteristics of these patients that differ from those who don’t have the disease
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| Odds Ratio | Probability that something will occur divided by probability it will not occur.
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| Kurtosis | Measure of peakedness in frequency distributions
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| platykurtic | lower, wider peak around the mean
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| leptokurtic | a more acute peak around the mean (bunching toward the mean)
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| skewness | a measure of the asymmetry of the probability distribution
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| positive skew | Tail to the right is longer
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| negative skew | Tail to the left is longer
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