Overview
This lecture covers special research designs, particularly longitudinal studies, and provides a framework for choosing research methods and ensuring study quality through reduced bias, control of variables, and generalizability.
Special Research Designs: Longitudinal Studies
- Longitudinal design involves measuring the same participants repeatedly over months or years.
- This design is valuable because each participant serves as their own control group, reducing extraneous variables.
- Longitudinal studies are especially useful for detecting long-term effects of interventions or changes.
- Challenges include high cost and participant retention over long periods.
Choosing a Research Design
- Use descriptive designs (e.g., observational, case study) when little is known about a topic.
- Apply correlational designs after basic exploration to identify relationships between variables.
- Experimental designs are used to test cause and effect by manipulating variables and controlling extraneous factors.
- Choose longitudinal studies to examine effects or changes over an extended period.
Key Considerations in Research Design
- Reduce bias by using reliable (consistent), valid (accurate), and precise measures.
- Eliminate alternative explanations by being systematic and controlling for known and unknown influences.
- Random assignment is the best method to control unknown variables in experiments.
- Determine generalizability (external validity) by assessing if results apply to the real world or specific populations/settings.
- Use representative samples to reflect the broader population of interest.
- Generalizability increases by replicating studies with different populations, settings, and times.
Key Terms & Definitions
- Longitudinal Design — A study where participants are measured repeatedly over an extended time.
- Control Group — A group used as a baseline comparison to evaluate effects in experimental designs.
- Internal Validity — The extent to which a study controls for extraneous variables and supports causal conclusions.
- External Validity (Generalizability) — The degree to which study findings apply to real-world scenarios or populations.
- Reliability — The consistency of a measurement across repeated uses.
- Validity — The accuracy of a measurement in capturing what it intends to measure.
- Random Assignment — Placing participants in groups by chance to minimize pre-existing differences.
Action Items / Next Steps
- Review main study designs and be prepared to apply them to research questions.
- Practice identifying which design is appropriate for different research scenarios.
- Ensure understanding of terms: reliability, validity, generalizability, internal and external validity.