Unit 3 Lesson 3: Experiments – Basic Principles

Experiments – Basic Principles

Unit 3, Topic 3.5: Experiments – Basic Principles

Overview

This lesson defines experiments as studies where researchers deliberately change one factor (the explanatory variable) to observe its direct effect on another (the response variable), which allows for claims about causation, unlike observational studies that can only suggest associations.
Example: Testing fertilizer on crop plots (manipulating treatment) to measure yield (response), claiming "Fertilizer causes higher growth," unlike watching fields without intervention.

Key principles to make experiments valid include control (using a comparison group to isolate the factor's effect), randomization (randomly assigning participants to groups to balance unknown influences), replication (repeating the experiment multiple times to check consistency and increase reliability), and blinding (hiding information about the treatment to prevent bias, with single blinding for participants only and double blinding for both participants and researchers).
Example: In a drug trial, control uses placebo; randomization assigns patients randomly; replication tests over weeks; single blinding hides drug from patients, double from doctors too.

Context, such as the population being studied and ethical considerations, is essential because it ensures the results are applicable and fair (e.g., testing a new learning app on diverse students helps generalize to real classrooms, but ignoring ethics like consent could invalidate claims). These principles work together to minimize bias and strengthen the experiment's ability to demonstrate cause-and-effect relationships.
Example: App test on mixed ages with consent generalizes to schools; randomization within groups cuts bias, proving "App boosts learning" ethically.

Assignment:

Part 1: Guided Practice Activity

Consider the example of testing a new energy drink's effect on running speed, with 50 runners divided into groups.
Follow the tasks below to define experiments and apply the principles.

Example Scenario: Measure running times before and after giving the drink to some runners and a placebo to others.

Tasks:

1. Defining Experiments:
   • Define what makes an experiment different from an observational study, and explain how it allows for causation claims.
     Example: Experiments actively manipulate a factor like the drink to test its impact on speed, enabling claims such as "The drink causes faster times," while observational studies only watch natural habits without control.
     
     
   • Extra Practice: For a scenario testing fertilizer on plant growth, define the experiment and note its causation potential.
     
     
2. Describing Key Principles:
   • Describe each principle: control, randomization, replication, and blinding (including single and double) - with a brief explanation of its role in the energy drink example. 
     Example:
     Control uses a placebo group to compare against the drink group, isolating the drink's effect;
     randomization assigns runners randomly to groups to even out fitness levels;
     replication tests multiple runners over days for consistent results;
     single blinding hides if it's the drink or placebo from runners, double blinding also hides it from timers to avoid influence.
     
     
   • Write 1-2 sentences on how these principles reduce bias and improve validity in the scenario.
     Example: Randomization and blinding reduce selection and expectation bias, while control and replication improve validity by ensuring differences are due to the drink, not chance or external factors.
     
     
     
3. Role Play Simulation (Individual):
   • Simulate assigning treatments for 10 runners (e.g., list numbers 1-10 and randomly assign 5 to drink/5 to placebo using a method like even/odd or coin flips).
     Example: Runners 1-10; even numbers (2,4,6,8,10) to drink group—this random split balances potential confounders like age.
     
     
   • Write 2-3 sentences describing your simulation process and how it applies the principles in context.
     Example: I used even/odd for randomization to fairly assign groups, incorporating control with placebo; this reduces bias in the running test by ensuring speed differences come from the drink, improving validity for athlete recommendations.

Part 2: Independent Practice

Design a simple experiment to test if background music improves math test performance, using 20 students and measuring scores.

Tasks:

• Define the experiment, including the manipulated factor and response variable, and explain how it supports causation claims.
• Describe all four principles (control, randomization, replication, blinding) and how you would implement each in this math test scenario.
• Simulate assigning treatments for 10 students 
• Write 2-3 sentences explaining how these principles reduce bias and improve the validity of your results.

Homework Assignment

• Brainstorm a real-world experiment idea (e.g., testing different snacks on focus during homework). Define the experiment, describe the four principles in detail with implementation steps, simulate assignment for 8 participants, and explain how they reduce bias to share next class.