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Non-experimental Designs

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Presentation on theme: "Non-experimental Designs"— Presentation transcript:

1 Non-experimental Designs
Psyc 231: Research Methods

2 Non-experimental Designs
Surveys Developmental Designs Small N Designs Quasi-experiments

3 Developmental Designs
Used to study development or changes in behavior Describe relationship between age and other variables Three main types Cross-sectional Longitudinal Cohort-sequential

4 Cross-sectional Designs
Uses a separate group of participants for each age group being compared Different groups measured once and compared to each other Between subjects design Most commonly used

5 Cross-sectional Designs
Study the development of memory over time All three age groups tested at one point in time Age 4 Age 7 Age 11

6 Cross-sectional Designs
Advantages Short period of time No real commitment Gather all data at one time

7 Cross-sectional Designs
Disadvantages Cohort/Generation effects Does not tell real development of individual Cannot infer causality

8 Longitudinal Designs Same participants are observed over time
Assesses stability of traits Individuals are compared to self throughout repeated measures over time Within subjects design

9 Longitudinal Designs Study of the development of memory over time
Same participants tested over time Age 4 Age 7 Age 11

10 Longitudinal Designs Advantages No generation effects
Examine individual differences Can see developmental changes

11 Longitudinal Designs Disadvantages Very time consuming and costly
Hard to find patient participants – Subject Attrition/Mortality Researchers lose interest Practice effects Cross-generational effects Conclusions based on members of one generation may not apply to other generations Cannot determine causality

12 Longitudinal Designs Wisconsin Longitudinal Study (WLS)
Began in 1957 and is still on-going (50 years) Originally studied plans for college after graduation Now it can be used as a test of aging and maturation

13 Cohort-sequential Designs
Measure groups of participants as they age Combines the best features of both longitudinal and cross-sectional designs Studies specific age groups over time Both between and within subjects design

14 Cohort-sequential Designs
Study of the development of memory over time Test multiple age groups over time Age 4 Age 8 Age 8 Age 12 Age 12 Age 16

15 Cohort-sequential Designs
Advantages Saves time Get more information Long-term effects and developmental changes Compare to different ages No generation effects

16 Cohort-sequential Designs
Disadvantages More time consuming than cross-sectional Does not mean causation

17 Small N Designs Study one or few participants (typically 3-8 participants) Each individual is analyzed separately Common type of design until 1920’s Still used in some areas of research: clinical settings, phenomenon Different from case studies

18 Small N Designs Typically observe participants Baseline studies
Effect doesn’t occur before IV (baseline) Show that effect occurs with IV (treatment) Doesn’t occur without IV (reversibility) Observation/testing generally occurs at 3 points Before treatment, after treatment, after reverse treatment Examine level and trend to determine effect

19 Small N Designs Level Trend How frequent or intense is the behavior?
Are the data points high or low? Trend Does the behavior increase or decrease? Are the data points flat or on a slope?

20 Small N Designs ABA design (baseline, treatment, baseline)
Must be able to reverse effect Could not have been due to maturation, history, etc. Effectiveness of a drug

21 Small N Designs Advantages Focus on individual performance
Can see big effects Avoid some ethical problems (non-treatments/controls) Allows to look at unusual (and rare) types of subjects Often used to supplement large N studies, with more observations on fewer subjects

22 Small N Designs Disadvantages Generalizability
Effects may be small relative to variability of situation Some effects are by definition between subjects Treatment can lead to a lasting change, so you don’t get reversals Ethical issues with reversing treatment

23 Small N Designs Hermann Ebbinghaus (1885) studied memory of nonsense syllables on himself Discovered the forgetting curve and learning curve Know a lot about memory today because of him

24 Quasi-experimental Designs
Almost “true” experiments but lack of control over assignment of participants Independent variable cannot be manipulated (inherent confound) Subject variable Time could be variable (Developmental) Random variable already present

25 Quasi-experimental Design s
Advantages Allows applied research when experiments not possible Threats to internal validity can (sometimes) be assessed Practical and more feasible than true experiments, especially in clinical settings Some generalizability

26 Quasi-experimental Designs
Disadvantages Difficult to make clear cause-and-effect statements Statistical analysis can be difficult Most statistical analyses assume randomness Can not randomize assignment to groups

27 Quasi-experimental Designs
Common types Non-equivalent control groups design Time series designs Interrupted time series design Control group interrupted time series design

28 Quasi-experimental Designs
Non-equivalent control groups design Typically used as a pretest-posttest Assignment based on already established variable Between subjects design participants Experimental group Control Measure Non-Random Assignment Independent Variable Dependent Variable

29 Quasi-experimental Designs
Non-equivalent control groups design: Pretest-posttest Example Individuals high on self-esteem and low on self-esteem Pretested on depression levels Intervention given to low self-esteem group Posttested on depression levels

30 Quasi-experimental Designs
Time series designs Interrupted times series design Observe on several occasions before and after the independent variable occurs Within subjects design obs obs obs Treatment obs obs obs The pretest observations allow the researcher to look for pre-existing trends The posttest observations allow the researcher to look for changes in the trends

31 Quasi-experimental Designs
Time series designs Control group interrupted time series design A variation of the interrupted time series designs Series of observations followed by treatment for experimental condition Compared to a control group obs obs obs Treatment obs obs obs obs obs obs obs obs obs

32 Questions?

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