Kinds of Quantitative Research: Essential Notes

Kinds of Quantitative Research

• Experimental

• Quasi-Experimental

• Pre-Experimental

• Non-Experimental: Survey (Descriptive, Correlational, Comparative)

Experimental Research

• Focus: cause-and-effect via manipulation of $IV$ and measurement of $DV$.

• Goal: only systematic difference between groups is the $IV$ level; all other variables held constant.

• Groups:

  • Experimental = receives $IV$ (treatment)

  • Control = no treatment (baseline)

Manipulating the Independent Variable

• Presence/absence technique – give treatment to one group, withhold from another.

• Amount technique – vary quantity (e.g., $1$ h, $2$ h, $5$ h).

• Type technique – vary kind of treatment (e.g., counselling A vs. B).

Quantitative Experimental Designs

True Experimental (all 3 present: treatment, control & random assignment)

• Pretest–posttest control group

• Posttest-only control group

• Solomon four-group (most robust; minimizes internal & external threats)

Key Validity Terms

• Internal validity – confidence that cause–effect is not due to other factors.

• External validity – generalizability of results to other settings.

Quasi-Experimental Research

• Missing either random assignment or control group.

• Chosen when randomization/control is unethical, costly, or impossible (e.g., smoking during pregnancy; birth order studies).

Non-Experimental Research

• Lacks treatment, control, and randomization.

Survey

• Self-report on attitudes, opinions, behaviors; describes current status.

Descriptive

• Portrays population with specific traits to understand it better.

Correlational

• Measures direction & strength of relationships; cannot infer causality or direction.

Comparative

• Examines similarities/differences between groups on a variable.

Quick Decision Guide (Quantitative Study)

1. Intervention present?

   • No $\Rightarrow$ Non-Experimental.

2. Control group present?

   • No $\Rightarrow$ Quasi-Experimental.

3. Random sample assignment?

   • Yes $\Rightarrow$ True Experimental.

   • No $\Rightarrow$ Quasi-Experimental.

Review Questions

• Name the two variables in an experiment.

• Identify the two basic groups.

• State the three $IV$ manipulation methods.

• When is research labeled quasi-experimental?

Final Reminder

There is no single "best" research design; choose the one that fits the question, ethics, and context.

Key Terms for Study

• Quantitative Research Kinds: Experimental, Quasi-Experimental, Pre-Experimental, Non-Experimental

• Experimental Research: Independent Variable ($IV$), Dependent Variable ($DV$), cause-and-effect, Experimental Group, Control Group

• IV Manipulation Methods: Presence/absence, Amount, Type

• True Experimental Designs: Pretest–posttest control group, Posttest-only control group, Solomon four-group

• Validity: Internal validity, External validity

• Quasi-Experimental Research: Missing random assignment/control group

• Non-Experimental Research: Lacks treatment, control, randomization

• Non-Experimental Sub-types: Survey, Descriptive, Correlational, Comparative

• Correlational Research: Cannot infer causality

• Decision Guide Factors: Intervention, Control group, Random sample assignment