Zoo212 - The Scientific Method L10 - Planning Experiments

The Scientific Method Overview

  • Date of Lecture: April 21, 2021

  • Course: Zoo212

  • Instructor: Professor Niall Vine

Planning Experiments

  • Objective: Understand the planning required to conduct experiments in scientific research.

  • Key Topics Covered:

    • Types of Experiments

    • Experimental Approaches

    • Principles of Designing an Experiment

    • Identifying Study Types

    • Data Sheet Design

    • Pre-Experiment Preparations

    • Sampling Considerations

What is a Scientific Experiment?

  • Definition: An organized and detailed series of steps to validate or reject a hypothesis.

Types of Experiments

  • Experimental: Direct manipulation and control of variables.

  • Quasi-experimental: Examines effects without random assignment.

  • Observational: Studies behaviors or conditions without interference.

Experimental Approaches

  • Laboratory Experiments:

    • Easily controlled settings.

    • Limited inference about real-world applications.

  • Natural Experiments:

    • Occur naturally without manipulation.

    • Weak conclusions due to lack of replication.

  • Field Experiments:

    • Manipulative treatments applied in natural environments.

  • Field Studies:

    • No random assignments; important but have limitations.

Deciding on Study Type

  • Experiment Study:

    • Mostly laboratory-based.

  • Correlation Study:

    • Often observation-based; field studies are a common example.

Principles of Designing an Experiment Study

  • Manipulation of Variables: Investigator artificially manipulates a variable within different groups to test effects.

  • Goal: Seek explanation rather than mere description.

Steps in Designing an Experiment

  1. Identify the Groups:

    • Start with a research hypothesis.

    • Based on the null hypothesis, determine required groups (Control vs Experimental).

    • Control Group: Not exposed to experimental treatment.

  2. Establish the Variables:

    • Clearly define independent and dependent variables.

    • Independent Variable: What you change (the cause).

    • Dependent Variable: What changes as a result (the effect).

    • Controlled Variables: Kept constant across all groups.

  3. Determine the Number of Replicates:

    • Minimum of three replicates for each group recommended.

    • More replicates enhance reliability; seek stable means and confidence intervals.

    • Typically aim for n ≈ 30 to avoid pseudoreplication.

  4. Randomise Subjects Across All Groups:

    • Ensure random assignment of subjects, not random selection.

    • Tools: Random number generators, coins, dice, Excel.

Principles of Designing a Correlation Study

  • Focus: A correlation study seeks the relationship between two or more variables.

  • Goal: Description rather than causation/itemization.

  • Key Steps:

    1. Establish variables for comparison.

    2. Determine the required number of replicates.

    3. Randomly allocate measuring equipment.

Next Steps After Designing the Experiment

  • Consider how to properly record data to ensure accurate results.