Scientific Passages: Deconstructing Experimental Design

Core Concepts

Covers the essential components of scientific methodology, including variables, control groups, and procedures, to help you understand how an experiment is constructed.

Scientific Passages: Deconstructing Experimental Design

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In a scientific experiment, what is the 'independent variable'?

The variable that the experimenter intentionally manipulates or changes to observe its effect. It is the 'cause' in a cause-and-effect relationship. On graphs, it's usually plotted on the x-axis.

What is the 'dependent variable'?

The variable that is measured or observed to see how it is affected by changes in the independent variable. It is the 'effect' in a cause-and-effect relationship and is usually plotted on the y-axis.

What is a 'control group' and what is its purpose?

A group in an experiment that does not receive the experimental treatment (the independent variable is not applied). Its purpose is to provide a baseline for comparison, allowing scientists to determine if the treatment actually had an effect.

What are 'controlled variables' or 'constants' in an experiment?

Factors that are kept the same for all groups (both experimental and control) throughout the experiment. This ensures that only the independent variable is influencing the dependent variable.

A study tests if a new fertilizer increases plant height. One group of plants gets the fertilizer, another gets none. Both get the same water, light, and soil. What is the independent variable?

The presence or absence of the new fertilizer. This is the factor that the researchers are intentionally changing between the groups.

In the fertilizer study (testing its effect on plant height), what is the dependent variable?

The plant height. This is the outcome that is being measured to see if the fertilizer had an effect.

In the fertilizer study (same water, light, and soil for all plants), what are the controlled variables?

The amount of water, the amount of light, and the type of soil. These are kept constant to ensure they don't interfere with the results.

Why is a large 'sample size' generally preferred in experiments?

A large sample size increases the reliability and statistical significance of the results. It helps ensure that the observed effects are not due to random chance or individual peculiarities in the subjects.

What is the difference between a 'controlled experiment' and an 'observational study'?

In a controlled experiment, researchers actively manipulate an independent variable. In an observational study, they simply observe subjects and measure variables without assigning treatments or intervening.

What information is typically found in the 'methodology' or 'procedure' section of a scientific account?

This section provides a step-by-step description of how the experiment was conducted, including the variables, the control and experimental groups, the sample size, and the tools used. It should be detailed enough for another scientist to replicate the study.

Why is 'replication'—repeating an experiment—a crucial part of the scientific process?

Replication helps to verify the results. If other scientists can repeat the experiment and get the same results, it increases confidence that the findings are accurate and not due to error, bias, or chance.

Scientific Passages: Deconstructing Experimental Design

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