Experimental Design: Variables, Hypothesis Testing

• Experimental design explores the cause-and-effect relationship between independent and dependent variables.
• The independent variable is manipulated, while the dependent variable is measured for changes.
• Scientists define variables, assign subjects, and measure the dependent variable during experiments.
• Experimental design tests a hypothesis under controlled conditions, limiting external interference.
• Outcomes of experimental investigations can support scientific laws and theories.
• A scientific theory explains why things happen, based on repeated experiments.
• Scientific law is a pattern, often in equation form, supported by experimental data.
• Experimental design is used across scientific disciplines for advancements.

What Makes a Good Experiment

• A good experiment requires background knowledge and proper equipment.
• Accurate equipment yields values close to the real value.
• Precise equipment yields measurements that are close to one another.
• Thoroughness and detail are key to a good experiment which should have both accuracy and precision.
• The scientific method is a standardized process for recording experiments.
• The scientific method enables reproducibility and validation of experimental results.
• Existing theories inform good experiment design.
• New theories emerge from experiments conducted using the scientific method.

Experimental Design Process

• The experimental design process uses procedures that are designed to test a hypothesis.
• The experimental design process involves defining variables, formulating a hypothesis, designing an experiment, assigning subjects, and measuring the dependent variable.
• A testable idea or hypothesis starts the experimental design process.
• Measurements must be accurate and precise to measure the outcome of the experiment.
• Data analysis involves graphs and tables to interpret results.
• Analysis focuses on data interpretation and its potential applications.

Step 1: Define Variables

• Defining variables is the first step of the experimental design process.
• Independent variables are changed by the experimenter.
• Dependent variables change in response to independent variables.
• Control variables are kept constant to prevent external influence on the experiment.
• Example: Testing plant growth under different colors of light.
• Independent variable: Color of light (red, green, yellow, blue).
• Dependent variable: Plant growth under each color.

Step 2: Formulating Hypotheses

• A hypothesis is an educated guess about the experiment's outcome.
• The purpose of a hypothesis is to be proven or disproven by the experiment's results.
• When formulating a hypothesis, you should make a statement.
• Example hypothesis: "If plants are exposed to different colors of light, they will grow at different rates."

Step 3: Experimental Design Science (Treatment and Control Group)

• Experiments include a treatment group undergoing the experimental change.
• A control group experiences no change or treatment, remaining under normal conditions.
• In the plant experiment:
  • Treatment group: Plants exposed to red, green, yellow, and blue light.
  • Control group: Plants exposed to sunlight.

Step 4: Assign Subjects

• Subject assignment can involve random selection and/or random assignment.
• Random selection picks a population for the experiment.
• Random assignment randomly assigns subjects to experimental or control groups.
• In the plant experiment, 50 plants are randomly assigned to different light colors.
• Example: 10 plants per group for red, green, yellow, and blue light.

Step 5: Measure the Dependent Variable

• Changes to the dependent variable are measured during the experiment.
• The independent variable is manipulated, and the resulting changes in the dependent variable are recorded.
• The collection of qualitative or quantitative values gathers results for the experiment. The plant experiment measures plant height in millimeters weekly for six months.
• Measurements are recorded in a data table for analysis

Example of an Experimental Investigation

• A pharmaceutical company tests the effectiveness of a new medication.
• The scientists select two groups of participants, the treatment group and the placebo group.
• The treatment group receives the medication.
• The placebo group receives a pill with no medicinal effect.
• Data collected confirms positive results in the treatment group, with no improvement in the placebo group.

Explore cause-and-effect relationships through experimental design. Learn about the roles of independent and dependent variables, hypothesis testing, and controlled conditions. Understand the importance of accurate and precise measurements and the relationship between experiments, scientific laws, and theories.