Understanding Ways to Collect Data (4)

Quantitative Research Designs

1. Experimental Research Designs

Experimental research is also known as longitudinal or repeated-measures studies. It is referred to as intervention research because researchers actively manipulate variables rather than just observe subjects. This design uses the scientific method to establish a cause-effect relationship among variables. A key feature of experimental research is control, where the researcher isolates variables to determine their effects.

Characteristics of Experimental Research

• Involves manipulation of an independent variable to determine its effects on dependent variables.
• Subjects are randomly assigned to experimental treatments rather than naturally occurring groups.
• A control group is used when the treatment effect may persist beyond initial measurements.

Key Differences from Descriptive Research

• Experimental research introduces a treatment and uses control methods to isolate its effects.
• Descriptive research only observes and records variables without manipulation.

Types of Experimental Designs

a. Pretest/Posttest Control Group Design

This design includes two groups:

• Control group: Receives no treatment.
• Experimental group: Receives treatment.

Both groups take a pretest and posttest for comparison.

Threats to validity:

• Maturation - subjects age or change over time.
• Test-wiseness - memorization of pretest affects posttest scores.
• Attrition - dropout of participants affects results.

b. Single-Group Pretest/Posttest Design

Used when there is a limited number of subjects. A single group undergoes:

1. Pretest
2. Treatment
3. Posttest

Threats to validity:

• Hawthorne Effect - subjects change behavior due to awareness of being studied.
• Maturation
• Attrition

c. Solomon Four-Group Design

Uses four equivalent groups to eliminate threats to validity.

Disadvantage: Requires a large number of participants.

Factors Affecting Experimental Research

• History – Events occurring between pretest and posttest (e.g., economic recession, natural disasters).
• Maturation – Changes in subjects over time (e.g., fatigue, boredom).
• Testing – Exposure to a pretest influences posttest responses.
• Mortality (Attrition) – Participants drop out, affecting group comparability.
• Interaction Effects – Extraneous variables (e.g., setting, time) distort results.
• Measuring Instruments – Changes in instruments, calibration, or scoring.
• Statistical Regression – Extreme scores tend to move toward the mean.
• Differential Selection – Pre-existing differences between groups impact results.
• John Henry Effect – Control group works harder when aware of being compared.

2. Survey Research

Survey research is the most widely used quantitative method in social sciences. It is used in censuses, public opinion polls, and market research.

Purpose of Surveys

• Collect standardized data from large samples.
• Analyze attitudes, beliefs, opinions, behaviors, or experiences.
• Gather both subjective (self-reported) and objective (fact-based) data.

Types of Survey Designs

a. Cross-Sectional Surveys

Collect data at a single point in time.

b. Longitudinal Surveys

Collect data over multiple points in time to measure change.

Challenges in Survey Research

• Attrition (participants dropping out).
• Response bias (participants may answer dishonestly).
• Sampling issues (ensuring a representative sample).