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# NU Research Methods

### Statistical Methods Flashcards 1

range length of the smallest interval which contains all the data
interquartile range (IQR) difference between the third and first quartiles
Variance amount of variation of all the scores for a variable s(square)=sum (x-mean(x))(square)/N
Standard Deviation square root of variance
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
Deviation x-x(mean)
Experimental research design a scientific control is used to minimize the unintended influence of other variables Random assignment of subjects
Quasi-experimental design Experimental method but without random assignment
When is quasi experimental design used? when randomization is impossible and/or impractical
Advantages of quasi experimental design Easier minimizes threats to external validity efficient in longitudinal research
Disadvantages of quasi experimental design Threats to internal validity Causal relationships difficult to determine Confounding variables
Internal validity extent to we can accurately state that the independent variable produced the observed effect
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
External validity Generalizability – to or across target populations – to or across tasks – to or across environments
Threats to external validity situation or environment Hawthorne effect (testing effect) Rosenthal effect Selection bias pre and post test effects
Hawthorne effect People act differently when they know they are being tested
Non-experimental design No control group Observational Used for theory development
cross tabulation A table of the frequency distribution of two or more variables
Null hypothesis hypothesis of no difference Something happens by chance or that no difference exists between populations
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)
Geometric mean used for data based on ratios, proportionate growth, percentage change.
differential attrition extent of subjects who drop out of a study AKA mortality
reliability consistency of observations not the same as validity (could be consistently false) reliability is necessary BEFORE validity can be established
Social desirability effect Subject respond in a way that appears favorable to the tester
Advantages of interviews higher response rate more lengthy and detailed more complex more flexible linking
Advantages of questionnaires low cost protectivity (confidential) less reactivity
reactivity act of measuring changes responses
Cohort study Compare group of people who share a certain characteristic (smokers) with unexposed group(non-smokers).
Experimental trial Exposed v. unexposed groups in trial setting (drug v. placebo)
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
Odds Ratio Probability that something will occur divided by probability it will not occur.
Kurtosis Measure of peakedness in frequency distributions
platykurtic lower, wider peak around the mean
leptokurtic a more acute peak around the mean (bunching toward the mean)
skewness a measure of the asymmetry of the probability distribution
positive skew Tail to the right is longer
negative skew Tail to the left is longer
Created by: 100000281586043