Variables & Controls - ACT Science

Define 'independent variable' in an experiment.

An independent variable is the variable that is changed or controlled in a scientific experiment. It's manipulated by researchers to observe its effect on other variables.
Identify the independent variable: Water temperature is changed; dissolved oxygen is measured.

Water temperature. This is the factor being deliberately manipulated.
What is the primary purpose of a double-blind experiment?

To prevent bias by ensuring neither participants nor researchers know who is receiving a treatment. It eliminates expectation effects that could bias results.
What is the effect of a confounding variable on experimental results?

It may distort the perceived effect of the independent variable on the dependent variable. It creates false correlations and misleading conclusions about causation.
What term describes variables other than the independent variable that can affect results?

Confounding variables. These are unwanted variables that can distort experimental results.
Identify the independent variable: Measuring reaction time under different light conditions.

Light condition. This is what researchers deliberately vary between test conditions.
What is a controlled variable (constant) in an experiment?

A factor kept the same across all trials. Prevents other factors from influencing the results.
What is a positive control?

A control expected to produce a known effect to verify the setup works. Confirms the experimental system is functioning properly.
What is a hypothesis in the context of variables?

A hypothesis is a proposed explanation for a phenomenon, predicting relationships between variables. It predicts how changing one variable affects another.
In an experiment, why is it crucial to have a well-defined control group?

To ensure that the results can be attributed to the experimental treatments rather than other factors. A proper control isolates the treatment effect from other influences.
What is blinding in an experiment?

Keeping subjects and/or researchers unaware of group assignments. Prevents expectations from influencing behavior and results.
What is the operational definition of a variable?

A precise description of how it is measured or manipulated. Makes the variable concrete and measurable for scientific study.
What distinguishes a control group from an experimental group?

A control group is not exposed to the independent variable, unlike the experimental group. Control groups don't receive the experimental treatment.
Identify the controlled variable: Comparing reaction rate at $20^ $ vs $30^ $ using same volume.

Solution volume. Volume must stay constant to isolate temperature's effect.
Which axis usually displays the dependent variable on a graph?

The $y$ -axis. Convention places the measured response on the vertical axis.
What is the role of randomization in controlling variables?

To reduce bias by evenly distributing confounding variables across groups. Random assignment prevents systematic differences between groups.
Identify one reason why controls are important in experiments.

They help ensure that the results are due to the independent variable. Controls eliminate alternative explanations for observed changes.
What does it mean to control a variable?

To control a variable means to keep it constant throughout the experiment. This prevents the variable from influencing results.
Find the dependent variable: A spring is loaded with different masses; extension is recorded.

Spring extension. Extension is the measured response to different masses.
What is the dependent variable in an experiment?

The measured outcome that responds to the independent variable. This is what changes in response to the independent variable manipulation.
Identify the independent variable: Studying the effect of diet on energy levels.

Diet type. This is what researchers deliberately change between groups.
What is the experimental group in an experiment?

The group receiving the treatment or manipulated condition. This group experiences the variable being tested.
Which variable is manipulated by the experimenter?

Independent variable. This is the factor researchers intentionally change or vary.
What is the best reason to include multiple levels of the independent variable?

To detect trends and estimate the relationship across a range. Reveals patterns and allows interpolation between tested values.
State the role of a control group in an experiment.

A control group is used as a baseline to compare results with the experimental group. It shows what happens without experimental treatment.
Identify the dependent variable: Effect of sunlight on plant height.

Plant height. This is what gets measured as the outcome variable.
What type of variable is 'age of participants' in a study on exercise?

Independent variable. Age is a factor that researchers can select or manipulate in their study design.
What is the purpose of using a placebo in experiments?

To serve as a control treatment to compare against the effects of the drug being tested. Placebos control for psychological effects unrelated to the actual drug.
What is the main goal of a controlled experiment?

To test the effect of an independent variable on a dependent variable while controlling other variables. Controls ensure that observed effects are due to the independent variable alone.
Identify the independent variable: Testing sound levels on plant growth.

Sound level. This is what researchers deliberately manipulate between groups.
What is a confounding variable?

A factor that changes with the independent variable and affects the dependent variable. Makes it difficult to determine what actually caused the observed effect.
Which variable is expected to change when the independent variable is altered?

Dependent variable. The dependent variable responds to changes in the independent variable.
Why is it important to have a control group?

It helps to isolate the effect of the independent variable by providing a comparison baseline. It shows what happens without the experimental treatment.
What is a confounding variable?

A confounding variable is an outside influence that changes the effect of a dependent and independent variable. It creates false relationships between variables being studied.
Identify the dependent variable: Water temperature is changed; dissolved oxygen is measured.

Dissolved oxygen concentration. This is the response being measured.
What is the difference between random assignment and random sampling?

Assignment places subjects in groups; sampling selects subjects from a population. Assignment creates comparable groups; sampling represents populations.
In a drug trial, which group receives a placebo?

Control group. The placebo group serves as a control for comparison.
Define a positive control.

A positive control is a group expected to produce a positive result, confirming that the experiment setup is capable of producing results. It proves the experimental system works as expected.
What is a confounding variable?

A confounding variable is an outside influence that changes the effect of a dependent and independent variable. It creates bias by affecting the relationship between variables being studied.
Which variable is measured in response to changes made by the experimenter?

Dependent variable. This variable shows the effect of experimental manipulation.
What is a negative control?

A control expected to show no effect to detect background changes. Helps identify unexpected changes not caused by the treatment.
Identify the independent variable: Plant growth with different fertilizers.

Type of fertilizer. This is what the experimenter deliberately changes between groups.
Identify the independent variable: Measuring learning with different study techniques.

Study technique. This is what researchers deliberately vary between groups.
What is the most common reason correlation does not imply causation?

A confounding variable may cause both observed changes. A third factor may independently influence both variables.
Identify the dependent variable: Different salt concentrations; time to boil is measured.

Time to boil. This is the response being measured.
In an experiment, what does a constant refer to?

A constant is a factor that does not change throughout the experiment. Constants ensure that only the independent variable affects the results.
What is the placebo effect?

A change caused by expectation rather than the treatment itself. Shows how beliefs alone can produce measurable effects.
What is a variable in a scientific experiment?

A variable is any factor, trait, or condition that can exist in differing amounts or types. It can be qualitative or quantitative and varies between subjects or conditions.
In a study on sleep and alertness, what is an independent variable?

Amount of sleep. Sleep amount is manipulated to observe its effect on alertness.
Identify the independent variable: A catalyst is present or absent; reaction time is measured.

Presence of the catalyst. Catalyst presence/absence is the manipulated condition.
What is an experimental group?

An experimental group is exposed to the independent variable to test its effect. This group receives the treatment being tested.
Identify the dependent variable: Analyzing the impact of sleep on memory retention.

Memory retention. This measures how well information is recalled.
Identify the confounder: Coffee intake and test scores correlate, but coffee drinkers sleep less.

Sleep amount. Sleep affects test performance independently of coffee intake.
Why is it important to control variables in an experiment?

To isolate the effect of the independent variable on the dependent variable. Control ensures observed changes are due to the intended treatment only.
Identify the variable type: Number of errors made on a test after sleep deprivation.

Dependent variable. Error count is measured as a response to sleep deprivation treatment.
What is replication in experimental design?

Repeating trials or experiments to check consistency of results. Increases confidence that results are not due to random chance.
How can random assignment help in an experiment?

It helps distribute confounding variables evenly across groups to minimize bias. Random assignment creates comparable groups and reduces selection bias.
What is a placebo?

An inert treatment used to mimic the experimental treatment. Controls for psychological effects of receiving treatment.
Identify the best control: Testing antibacterial soap; what should the comparison group use?

Non-antibacterial soap (or no soap), otherwise identical procedure. Tests soap effect while controlling for washing action.
What is the purpose of having a control group in an experiment?

To provide a standard for comparison against the experimental group. It establishes a baseline to determine if the treatment has an effect.
Identify the variable type: Amount of fertilizer used in a plant growth experiment.

Independent variable. Fertilizer amount is manipulated to test its effect on plant growth.
Which type of variable is measured to assess the effect of the independent variable?

Dependent variable. This variable responds to changes in the independent variable.
What is a control group?

A control group is a group in an experiment that does not receive the experimental treatment. It serves as a baseline for comparison with the experimental group.
Define a negative control.

A negative control is a group where no response is expected, ensuring that the experimental setup does not produce false positives. It confirms no response occurs without treatment.
What is the main characteristic of a control variable?

It is kept the same throughout the experiment. Consistency eliminates it as a source of variation in results.
Which axis should show temperature if you measure temperature as time passes?

The $y$ -axis. Temperature is the measured response to time.
What is a dependent variable?

A dependent variable is the variable being tested and measured in a scientific experiment. This responds to changes in the independent variable.
Which axis usually displays the independent variable on a graph?

The $x$ -axis. Convention places the manipulated variable on the horizontal axis.
Identify the dependent variable: Testing the effect of temperature on enzyme activity.

Enzyme activity. This measures how enzymes respond to temperature changes.
Which axis should show time if you measure temperature as time passes?

The $x$ -axis. Time is the manipulated variable affecting temperature.
In an experiment, which variable is deliberately held constant?

Control variable. It's kept constant to prevent interference with the experimental results.
What is an independent variable?

An independent variable is the variable that is changed or controlled in a scientific experiment. This is the factor deliberately manipulated by researchers.
Identify the dependent variable: Measuring the effect of exercise intensity on pulse rate.

Pulse rate. This measures the cardiovascular response to activity.
Identify the independent variable: Plants get $0$ , $5$ , or $10$ mL fertilizer; height is measured.

Fertilizer amount (mL). This is the variable deliberately changed across groups.
What type of variable is 'type of food' in a study on its effect on energy levels?

Independent variable. Food type is the factor manipulated to observe its effect on energy.
Identify the dependent variable: A catalyst is present or absent; reaction time is measured.

Reaction time. Reaction time is measured to assess catalyst effect.
Define a control variable.

A control variable is a factor that is kept constant to prevent its influence on the outcome. Maintaining constancy prevents it from affecting experimental results.
Identify the independent variable: Different salt concentrations; time to boil is measured.

Salt concentration. This is the variable being deliberately changed.
What type of variable is 'amount of caffeine consumed' in a study on alertness?

Independent variable. Caffeine amount is manipulated to test its effect on alertness.
Identify the independent variable: Studying the effect of fertilizer on plant color.

Fertilizer type. This is what researchers deliberately change between groups.
Identify the variable type: Reaction time in response to a stimulus.

Dependent variable. Reaction time is measured as a response to the stimulus treatment.
Identify the type of variable: Speed of a car measured after applying different brakes.

Dependent variable. Speed is measured as a response to the brake type treatment.
Which variable should be controlled: Enzyme rate vs pH using the same enzyme mass each time?

Enzyme concentration (or mass). Different amounts would confound the pH effect on rate.
Which variable is not affected by other variables in the experiment?

Independent variable. It's manipulated by the researcher and influences other variables.
Identify the variable type: Temperature measured during a reaction.

Dependent variable. Temperature is measured as a response to experimental conditions.
Identify the dependent variable: Plants get $0$ , $5$ , or $10$ mL fertilizer; height is measured.

Plant height. This is what's measured to assess the fertilizer's effect.
Identify the control variable: Testing the effect of sugar concentration on fermentation rate.

Type of yeast. Sugar concentration varies, so yeast type stays constant.
Which variable should be controlled: Testing light intensity on photosynthesis using identical plants?

Plant species (use the same species for all groups). Different species could respond differently to light intensity.
What is the control group in an experiment?

The baseline group not receiving the experimental treatment. Provides a comparison to show what happens without the treatment.
What is the purpose of a control in an experiment?

To provide a standard for comparison and ensure that the experiment is fair and unbiased. Controls eliminate alternative explanations for observed results.
Identify the variable that must be held constant: Comparing battery brands by flashlight brightness.

Same flashlight and bulb. Different equipment could affect brightness measurements.
Identify the variable type: Amount of sunlight a plant receives in a growth study.

Independent variable. Sunlight is manipulated by the researcher to test its effect on growth.
What is the main purpose of controlling variables?

To isolate the effect of the independent variable on the dependent variable. Ensures observed changes are truly caused by the independent variable.
In an experiment, what type of variable is the environment maintained at a constant temperature?

Control variable. Constant temperature eliminates environmental variation as a factor.
What role do constants play in an experiment?

Constants ensure that the experiment tests only the effect of the independent variable on the dependent variable. They prevent unwanted variables from affecting outcomes.
What is the term for a variable that is not controlled and affects the outcome?

Confounding variable. Uncontrolled variables can create false conclusions about cause and effect.
Identify the dependent variable: Testing the effect of water pH on fish health.

Fish health. This measures the organism's response to environmental changes.
In an experiment, what does the dependent variable depend on?

The changes made to the independent variable. The dependent variable responds to manipulations of the independent variable.
Identify the control variable: Testing the effect of humidity on paper strength.

Type of paper. Humidity varies, so paper type must stay constant.
In a study of the effect of temperature on solubility, identify the independent variable.

Temperature. Temperature is the factor being manipulated to test its effect.
Find the independent variable: A spring is loaded with different masses; extension is recorded.

Mass (or applied force). Mass is what's deliberately varied to test spring response.
What is random assignment used for in experiments?

To reduce bias by distributing confounders across groups. Ensures groups are comparable by equalizing unknown factors.
Identify the control group: A drug is tested; one group receives a placebo.

The placebo group. This group receives no active drug for comparison.
Which type of variable is manipulated by the researcher?

Independent variable. Researchers deliberately change this variable to test its effects.
What is a variable in an experiment?

A variable is any factor, trait, or condition that can exist in differing amounts or types. This includes anything measurable that can change during research.
Identify the control variable: Testing plant growth in various soil types.

Plant species. Soil type varies, so plant species must remain constant.
What is the relationship between independent and dependent variables?

The independent variable is changed to observe its effect on the dependent variable. Changes in the independent variable cause changes in the dependent variable.
What is a trial in an experiment?

One run or repetition of the procedure. Multiple trials help ensure results are reliable and repeatable.
Find the independent variable: Studying effect of caffeine on sleep duration.

Caffeine intake. This is the factor being deliberately varied in the study.
What is the independent variable in an experiment?

The factor intentionally changed by the experimenter. This is what the researcher deliberately manipulates to test its effect.
What is the significance of random assignment in experiments?

Random assignment reduces bias and ensures that any differences are due to the independent variable. It ensures groups are equivalent before treatment begins.
Find the dependent variable: Investigating the impact of exercise on heart rate.

Heart rate. This measures the body's response to physical activity.
Identify the role of controls in an experiment.

Controls are used to minimize the effects of variables other than the independent variable. They isolate the effect of the independent variable by keeping other factors constant.
What is an experimental group?

The experimental group receives the test variable in an experiment. It's exposed to the treatment being tested in the study.
Define a controlled experiment.

A controlled experiment tests the effect of a single variable while keeping others constant. Only one variable changes while others remain constant.
Identify the control variable: Testing the effect of salt concentration on plant growth.

Plant species. Salt concentration varies, so plant species stays constant.
Identify the dependent variable: Analyzing the impact of diet on weight loss.

Weight loss. This measures the outcome researchers want to study.

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