Experimental Design - ACT Science

Which option best supports causation: manipulating light intensity or only observing natural light levels?

Manipulating light intensity. Manipulation allows testing cause-effect relationships.
Define the term 'sample size' in research.

The number of subjects included in a study. Larger samples generally provide more reliable and generalizable results.
Identify the purpose of a control group in an experiment.

To provide a baseline for comparison with the experimental group. Shows what happens without treatment for fair comparison.
State the purpose of a placebo in experiments.

To eliminate bias by mimicking the experimental treatment. It prevents participants from knowing if they received real treatment.
Identify the group that receives the treatment in an experiment.

Experimental group. This group gets the treatment being tested.
What is double-blind procedure in an experiment?

Neither subjects nor evaluators know group assignments. Eliminates bias from both sides of study.
State one way to minimize bias in experiments.

Use of double-blind procedures. When neither group knows treatment status, expectations can't influence outcomes.
What is the significance level in hypothesis testing?

The probability of rejecting a true null hypothesis. It sets the threshold for determining statistical significance.
Which design change best controls a confounder: keep temperature constant or measure it once?

Keep temperature constant. Control eliminates temperature as confounding variable.
Find the independent variable: A study on exercise's effect on sleep quality.

Exercise. Exercise is the factor being manipulated to see its impact.
Which variable is the outcome or response variable in an experiment?

Dependent variable. This measures what happens due to treatment.
Which option best increases reliability: perform more trials or change the hypothesis?

Perform more trials. More trials average out random errors.
What is a source of systematic error in an experiment?

A consistent bias that shifts measurements in one direction. Creates predictable deviation from true values.
What does it mean to 'operationalize' a variable in research?

To define it in practical, measurable terms. Makes abstract concepts concrete and testable.
What is an operational definition in experimental design?

A variable definition stated in measurable, specific procedures. Ensures consistent, objective measurement methods.
Define 'systematic error' in experimental design.

Consistent, predictable error that affects measurements. Unlike random error, systematic error creates consistent bias in one direction.
What is the purpose of random sampling in experiments?

To ensure that each member of the population has an equal chance of selection. Prevents selection bias in choosing participants.
Which option best matches a negative control: a condition expected to produce no effect?

A condition expected to produce no response. Confirms no false positive responses occur.
What is a positive control in experimental design?

A condition known to produce an effect to verify the setup works. Verifies experimental system is functioning properly.
Identify the best way to test one factor at a time when studying two variables.

Hold one variable constant while varying the other. Isolates effects of individual variables.
Identify the independent variable: plants receive $0$ , $5$ , or $10$ mL fertilizer daily.

Daily fertilizer volume. The researcher controls fertilizer amount.
Identify a key feature of quantitative data in experiments.

Numerical and can be measured. Allows statistical analysis and precise comparisons.
What is the purpose of a pilot study?

To test the feasibility and refine the methodology. Small-scale trial identifies potential problems early.
What distinguishes qualitative from quantitative data?

Qualitative is descriptive; quantitative is numerical. Qualitative uses words/categories while quantitative uses numbers/measurements.
What is a pilot study?

A small-scale preliminary study to evaluate feasibility. It tests procedures and identifies potential problems before the full study.
What is meant by 'external validity' in experiments?

The extent to which results generalize to other contexts. High external validity means results apply beyond the specific study conditions.
Identify a potential confounding variable: Studying the effect of sleep on memory.

Stress levels. Stress could independently affect memory, creating alternative explanations.
What is the effect of increasing sample size in an experiment?

Increases reliability and reduces sampling error. Larger samples better represent the target population.
Which method ensures that experimental results are not biased?

Randomization. Random assignment eliminates systematic differences.
Which aspect of an experiment is manipulated by the researcher?

Independent variable. The researcher controls this to test its effects.
What is an experimental group?

The group receiving the treatment under investigation. This group receives the actual treatment being tested for effectiveness.
What is a confounding variable?

A variable that influences both independent and dependent variables. It creates alternative explanations for observed results.
What is the importance of an operational definition in research?

Defines how variables are measured and observed. Ensures consistent measurement across all studies.
What is random sampling, and what does it primarily improve?

Selecting subjects by chance; it improves population representativeness. Makes results generalizable to the population.
What is random assignment in experimental design?

Randomly allocating participants to different groups. This ensures groups are equivalent before treatment begins.
Identify the measurement type: recording mass as $12.4$ g.

Quantitative. Mass measurement provides numerical data.
Identify the variable measured in an experiment to assess the effect of manipulation.

Dependent variable. This shows the effect of the manipulation.
Which type of variable can potentially confound the results of an experiment?

Confounding variable. These create alternative explanations for results.
What kind of variable is manipulated to observe effects on the dependent variable?

Independent variable. This is what the researcher changes or controls.
What is a 'confounding variable' in an experiment?

An extraneous variable that affects the outcome, obscuring results. Makes it impossible to determine true cause of results.
What is a sample size, and why does it matter?

Number of subjects/observations; larger sizes reduce random error. More data points increase statistical reliability.
What is the advantage of using a factorial design in experiments?

Allows examination of interactions between variables. Tests multiple variables simultaneously for efficiency.
What can be concluded about causation from a correlational study?

Correlation does not establish causation. Association alone cannot prove one causes another.
What is the role of statistical analysis in experimental design?

To determine the significance of results. Determines if results are due to chance or treatment.
Identify the experimental group: Testing a new teaching method vs. traditional.

Group using the new teaching method. This group receives the new method being evaluated.
Identify one advantage of a repeated measures design.

Reduces variability by using the same subjects. Each person serves as their own control.
What is the dependent variable in an experiment?

The measured outcome that responds to the independent variable. This outcome is observed to see if it changes.
Define 'placebo effect' in experimental terms.

Changes in outcomes due to participants' expectations. Believing you received treatment can cause real physiological changes.
What is a placebo in experimental design?

An inert treatment used to mimic the experimental treatment. Controls for psychological effects of treatment.
What is a dependent variable in an experiment?

A variable that is measured and affected in the experiment. This is the outcome or response being studied.
What is a 'single-blind' experiment?

Participants do not know their group assignment. Only participants are unaware of their group.
What is the purpose of blinding in experiments?

To prevent bias from influencing results. When participants don't know their group, expectations can't skew results.
Which option best increases precision: use a more sensitive instrument or add a placebo?

Use a more sensitive instrument. Better instruments reduce measurement uncertainty.
Identify the design flaw: different thermometers are used for each treatment group.

Instrument difference introduces systematic bias. Different instruments create systematic measurement bias.
What is a quantitative measurement in data collection?

A numerical measurement with units. Provides precise, measurable data for analysis.
What is an independent variable in an experiment?

A variable that is manipulated to observe its effect. This is the cause or input that researchers control.
What is replication in experimental design?

Repeating trials or using multiple subjects to confirm results. Increases reliability and statistical power.
What is the role of a control group?

To serve as a baseline for comparison. Without a control, you can't determine if changes are due to treatment.
What is an experimental group in an experiment?

A group that receives the treatment or manipulated condition. Used to test the effect of the treatment.
Identify one method to minimize bias in experimental results.

Randomization. Random assignment is most effective bias control.
What is the primary goal of random sampling?

To ensure every individual has an equal chance of selection. This prevents sampling bias and increases representativeness.
What does it mean if an experiment is 'controlled'?

Variables are regulated to prevent confounding effects. Eliminates alternative explanations for results.
What is a qualitative observation in data collection?

A descriptive, non-numerical observation. Describes qualities without numerical values.
What is a hypothesis in scientific research?

A testable prediction about the relationship between variables. Must be specific and measurable to test scientifically.
What is a sampling bias?

A bias in which the sample is not representative. The sample doesn't accurately reflect the larger population of interest.
Identify the dependent variable: Studying the effect of light on photosynthesis.

Rate of photosynthesis. This is the measured response to different light conditions.
What is the difference between accuracy and precision?

Accuracy: closeness to true value; precision: repeatability. Two different aspects of measurement quality.
Identify the controlled variable: enzyme rate tested at pH $4$ , $7$ , $10$ using same enzyme amount.

Amount (concentration) of enzyme. Same enzyme amount isolates pH effects.
Which option best reduces bias: random assignment or choosing volunteers?

Random assignment. Random assignment eliminates selection bias.
Define a dependent variable in experimental design.

The variable that is measured or observed. This is what changes in response to the independent variable.
What is the primary purpose of repeating trials in an experiment?

To increase reliability by reducing the impact of random error. Multiple measurements average out random variations.
Identify the independent variable: Experiment on diet effects on blood sugar.

Diet. Diet is the variable being manipulated to observe blood sugar changes.
Which option is the clearest operational definition of "growth"?

Increase in height in cm over $7$ days. Specific, measurable criteria define the variable.
State the main benefit of using a large sample size.

Increases the reliability and generalizability of results. Larger samples reduce random variation and increase statistical power.
What is a 'between-subjects' design?

Different subjects are used in each condition. Separate groups reduce individual differences effect.
What can be concluded about causation from a well-controlled experiment?

A causal relationship can be supported if confounders are controlled. Control eliminates alternative explanations for results.
What is an operational definition in experimental terms?

A clear, precise description of how variables are measured. This ensures researchers measure variables consistently and objectively.
Identify the dependent variable: Testing fertilizer's effect on plant growth.

Plant growth. Plant growth is the outcome being measured in response to fertilizer.
What is random error in an experiment?

Unpredictable variation that causes scatter in repeated measurements. Causes data points to spread around true value.
How does blinding reduce bias in an experiment?

Prevents expectations from influencing results. Eliminates unconscious influence on data collection.
What is meant by 'random error' in experiments?

Error that varies unpredictably between measurements. Random error creates variability but doesn't consistently bias results.
What is the significance of a control condition in experiments?

Serves as a comparison to evaluate the effect of treatment. Shows whether treatment actually made a difference.
Identify the dependent variable: plants receive $0$ , $5$ , or $10$ mL fertilizer; height is recorded.

Plant height. Height responds to fertilizer treatment.
Define 'null hypothesis' in research terms.

A statement that there is no effect or difference. It assumes no treatment effect exists until evidence proves otherwise.
What is the main difference between an experiment and an observational study?

Experiments manipulate variables; observational studies do not. Only experiments can establish cause-effect relationships.
What is a potential limitation of experimental design?

May not reflect real-world conditions. Artificial settings may not match real life.
Identify the measurement type: recording color change as "blue" or "green".

Qualitative. Color categories are non-numerical observations.
What is the primary purpose of keeping a control group?

To provide a baseline for comparison to the treatment condition. Shows what happens without the treatment.
Which option best indicates a controlled experiment: only one variable changes between groups?

Only the independent variable differs between groups. Single variable change isolates cause-effect relationships.
Identify the confounder: exercise group also changes diet, but diet is not tracked.

Diet change. Uncontrolled variable that affects the outcome.
Identify the control group: Testing a new medication vs. placebo.

Placebo group. The placebo group provides the comparison baseline for the medication group.
Define 'external validity' in the context of experiments.

The extent to which results generalize to other settings. How well findings apply beyond the study setting.
What type of graph is best for showing changes over time?

Line graph. Shows trends and patterns in continuous data.
What is the main purpose of replication in experiments?

To confirm the reliability and validity of results. Repeated studies help establish whether findings are consistent and trustworthy.
What is the control group in an experiment?

The baseline group without the experimental treatment. Provides comparison to show treatment effects.
What is a hypothesis test in the context of research?

A method to determine if there is a significant effect. It uses statistical analysis to determine if observed differences are meaningful.
Identify the dependent variable: Testing fertilizer's effect on crop yield.

Crop yield. Crop yield is the outcome measured to assess fertilizer effectiveness.
What characterizes a double-blind experiment?

Neither participants nor researchers know group assignments. This prevents both participant and researcher bias from affecting results.
Define 'randomization' in the context of experimental design.

Assigning subjects to groups by chance to reduce bias. Ensures each participant has equal chance of any group.
What is the primary goal of experimental design?

To establish a cause-and-effect relationship. Proper experimental control allows researchers to infer causation, not just correlation.
What is a hypothesis in experimental design?

A testable statement predicting an outcome. It guides research by making predictions that can be tested through experimentation.
What is meant by 'double-blind' in experiments?

Neither participants nor researchers know group assignments. Prevents bias from expectations of both groups.
Identify the best control for a drug study: compare to no treatment, placebo, or higher dose only.

Placebo. Placebo controls for psychological effects.
What is blinding (single-blind) in an experiment?

Subjects do not know which treatment group they are in. Prevents placebo effects from biasing results.
What does 'internal validity' refer to?

The extent to which an experiment avoids confounding. High internal validity means the experiment properly isolates cause and effect.
Identify the control group: drug trial compares drug vs sugar pill.

The sugar pill (placebo) group. No active treatment provides baseline comparison.
What is the benefit of using a placebo in control groups?

To isolate the effect of the treatment itself. Separates psychological effects from actual treatment.
Which option best reduces experimenter bias: double-blind procedure or larger beakers?

Double-blind procedure. Prevents conscious or unconscious researcher bias.
Identify the independent variable in an experiment.

The variable that is manipulated by the researcher. This is what the experimenter changes to test its effect.
Identify the control group: Testing a new drug vs. placebo.

Placebo group. The placebo group receives no active treatment for comparison.
What is meant by experimental validity?

The degree to which an experiment measures what it intends to. Valid experiments accurately test their hypotheses without confounding factors.
Identify the role of a placebo in an experiment.

A harmless substance given to control group to mimic treatment. Controls for psychological effects of receiving treatment.
What is the independent variable in an experiment?

The factor deliberately changed by the researcher. This variable is manipulated to test its effect.
Identify the independent variable: Study on caffeine's effect on alertness.

Caffeine. Caffeine is the factor being varied to test its impact on alertness.
What does 'replication' mean in scientific research?

Repeating an experiment to verify results. Confirms findings are consistent and reliable.
What is a controlled variable in an experiment?

A factor kept constant across all experimental conditions. These prevent confounding effects from other variables.
What is a 'null hypothesis' in the context of an experiment?

A statement that there is no effect or difference. Assumes no relationship exists between variables.
What is a 'within-subjects' design?

Same subjects are used in all treatment conditions. Controls for individual differences between participants.
Define reliability in the context of experimentation.

The consistency of a measure across trials. Reliable measures produce similar results when repeated under same conditions.
What strategy is used to minimize the placebo effect in an experiment?

Double-blind procedure. Neither group knows treatment status to prevent bias.
Identify the best reason to randomize trial order when testing multiple temperatures.

To reduce order effects and time-related confounding. Random order prevents time-dependent confounding.
Why is it important to have a large sample size in an experiment?

To increase the generalizability of results. Results apply more broadly with diverse samples.

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