What this area covers
- The scientific method as a sequence
- Independent, dependent and controlled variables
- The role of a control group
- Evaluating whether a conclusion follows from the data
- Measurement tools and accuracy versus precision
- Identifying sources of error
Concepts that come up most in our question bank:
Where students lose marks
Independent and dependent variables get swapped constantly. The independent variable is the one the researcher changes; the dependent is what gets measured in response.
How to study it
Phrase every experiment as a sentence: "if I change X, then Y will happen." X is independent, Y is dependent, and everything held steady is a control. Questions about validity almost always come down to whether something other than X could explain the change in Y.
Practice questions
Answer these, then check them to see the full explanation for every option — including why each wrong answer is wrong.
- Question 1
A scientist measures the same sample five times and gets results of 4.52, 4.51, 4.53, 4.52, and 4.51. These measurements demonstrate high:
Correct answer: B. Precision refers to how close repeated measurements are to each other (consistency/reproducibility). These five values are very close together (range of only 0.02), showing high precision. Note: precision does not tell us if the measurements are close to the true value (that would be accuracy).
- A. Accuracy describes how close measurements are to the true (actual) value. Without knowing the true value, we can assess precision but not accuracy.
- C. Bias is a systematic error that consistently skews results in one direction. Consistent results could be precise but biased if the true value is different.
- D. Random error causes measurements to scatter unpredictably. These measurements are very consistent, suggesting low random error.
- Question 2
Which of the following is a testable hypothesis?
Correct answer: B. A testable hypothesis is a specific, measurable prediction that can be supported or refuted through experimentation. This hypothesis identifies the independent variable (hours of sunlight), dependent variable (plant height), and makes a measurable prediction (taller growth).
- A. 'Plants are beautiful' is a subjective opinion that cannot be measured or tested scientifically.
- C. 'Best color' is a subjective opinion, not a measurable, testable claim.
- D. 'Most important emotion' is a value judgment that cannot be experimentally tested.
- Question 3
A researcher finds that students who eat breakfast score higher on tests. She concludes that eating breakfast causes higher test scores. What is the flaw in this conclusion?
Correct answer: B. The researcher found a correlation (association) between breakfast and test scores but concluded causation. Other factors (confounding variables) such as socioeconomic status, sleep quality, study habits, and parental involvement could explain both breakfast eating and higher scores. Only controlled experiments can establish causation.
- A. A larger sample size generally strengthens a study, not weakens it. Sample size is not the flaw here.
- C. Test scores are routinely and reliably measured in educational research.
- D. Research does suggest breakfast can affect cognitive performance. The issue is not whether breakfast matters but whether this study design can prove it.
- Question 4
In an experiment testing a new drug, one group receives the drug and another receives a sugar pill that looks identical. The sugar pill is called a:
Correct answer: B. A placebo is an inactive treatment (like a sugar pill) that looks identical to the actual treatment. It is given to the control group to account for the placebo effect — the tendency for patients to feel better simply because they believe they are receiving treatment.
- A. A catalyst is a substance that speeds up a chemical reaction. It is a chemistry term, not an experimental design term.
- C. A variable is any factor that can change in an experiment. While the treatment type is a variable, the sugar pill itself is specifically called a placebo.
- D. A hypothesis is a testable prediction, not a physical substance used in an experiment.
- Question 5
A study reports that a new medication reduces blood pressure by an average of 5 mmHg compared to placebo (p = 0.03). What does the p-value indicate?
Correct answer: B. A p-value of 0.03 means there is a 3% probability that the observed difference (5 mmHg reduction) would have occurred by random chance if the medication had no real effect. Since p < 0.05 (the conventional threshold), the result is considered statistically significant.
- A. The p-value does not indicate the probability that the treatment works. It indicates the probability of the results occurring by chance.
- C. The p-value is not a response rate. Response rates are reported separately.
- D. The 5 mmHg reduction is the effect size, not related to the p-value of 0.03.
- Question 6
Which of the following best describes a scientific theory?
Correct answer: B. In science, a theory is not a guess — it is a well-tested, well-supported explanation for a set of observations or phenomena, backed by extensive evidence from many experiments and observations. Examples: theory of evolution, germ theory of disease, atomic theory.
- A. A guess or untested prediction is a hypothesis, not a theory. Theories have been extensively tested and supported.
- C. A single experiment produces data, not a theory. Theories are supported by many experiments over time.
- D. An untested idea is a hypothesis. Theories have been rigorously tested and confirmed by multiple lines of evidence.
- Question 7
A researcher studies whether caffeine affects reaction time. She gives Group A 200 mg of caffeine and Group B a decaf placebo, then measures reaction times. What is the dependent variable?
Correct answer: B. The dependent variable is what is measured as the outcome — in this case, reaction time. It 'depends' on the independent variable (caffeine vs. placebo). The researcher measures whether reaction times differ between the caffeine and placebo groups.
- A. The amount of caffeine (200 mg vs. 0 mg) is the independent variable — the factor being manipulated by the researcher.
- C. The number of participants is part of the experimental design but is not a variable being tested.
- D. The type of placebo is part of the experimental setup (a controlled element), not the dependent variable.
- Question 8
Which of the following would introduce bias into a research study?
Correct answer: B. When participants self-select into groups, it introduces selection bias — those who choose treatment may differ systematically from those who choose control (in motivation, severity of illness, health consciousness, etc.). Random assignment prevents this by distributing these differences evenly across groups.
- A. Randomized controlled trials are specifically designed to minimize bias through random group assignment.
- C. Double-blind methodology reduces bias by preventing both participants and researchers from knowing who receives the treatment.
- D. A large, diverse sample improves generalizability and reduces sampling bias.
- Question 9
A graph shows a straight line going upward from left to right. This indicates:
Correct answer: B. An upward line from left to right shows a positive correlation — as one variable increases, the other also increases. The steeper the line, the stronger the relationship.
- A. A negative correlation would show a downward line from left to right (as one increases, the other decreases).
- C. No relationship would show randomly scattered data points with no clear pattern or trend.
- D. An upward trend is a valid result, not a failure. It tells us the variables are positively related.
- Question 10
What is the purpose of a control group in an experiment?
Correct answer: B. The control group does not receive the experimental treatment and serves as a baseline. By comparing the experimental group's results to the control group, researchers can determine whether observed changes are due to the treatment or other factors.
- A. The control group receives no treatment (or a placebo). The experimental group receives the treatment being tested.
- C. Sample size is important but is determined by the number of participants, not the control group's existence.
- D. Variables cannot be entirely eliminated. Controlled variables are kept constant, but the control group's purpose is comparison, not elimination of variables.
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