BAPSY Psychological Research and Statistics 2 — Questions and Answers
Question 1: A researcher finds p = 0.03 with a small effect size (d = 0.15). What is the most accurate interpretation?
- The result is statistically significant but may lack practical significance (Correct answer)
- The result is both statistically and practically significant
- The result is practically significant but not statistically significant
- The small effect size invalidates the statistical test
Correct answer: The result is statistically significant but may lack practical significance
Statistical significance (p < 0.05) does not guarantee practical importance; a tiny effect in a large sample can be significant yet trivial.
Question 2: Which sampling method divides the population into subgroups and randomly samples from each in proportion to their size?
- Cluster sampling
- Systematic sampling
- Stratified random sampling (Correct answer)
- Convenience sampling
Correct answer: Stratified random sampling
Stratified random sampling ensures proportional representation of subgroups by randomly selecting from each stratum.
Question 3: In a 2×3 factorial ANOVA, how many main effects and interactions are tested?
- 1 main effect and 1 interaction
- 2 main effects and 1 interaction (Correct answer)
- 3 main effects and 2 interactions
- 2 main effects and 3 interactions
Correct answer: 2 main effects and 1 interaction
A 2×3 factorial ANOVA tests two main effects (one per factor) and one two-way interaction.
Question 4: What does a 95% confidence interval represent?
- There is a 95% probability the true parameter falls in this specific interval
- If repeated sampling were done, 95% of such intervals would capture the true parameter (Correct answer)
- The sample mean has a 95% chance of being correct
- 95% of data points fall within this range
Correct answer: If repeated sampling were done, 95% of such intervals would capture the true parameter
A confidence interval is a frequentist statement about the long-run behavior of the procedure, not the probability for a single interval.
Question 5: Which threat to internal validity occurs when participants are tested multiple times and improve due to familiarity with the test?
- Maturation
- History
- Testing effect (Correct answer)
- Regression to the mean
Correct answer: Testing effect
The testing effect (also called practice effect) occurs when repeated exposure to the same measure improves scores independent of the treatment.
Question 6: A Pearson r = –0.72 between stress and immune function means:
- Stress causes decreased immune function
- Higher stress is associated with lower immune function (Correct answer)
- Immune function predicts stress levels
- The relationship explains 72% of variance
Correct answer: Higher stress is associated with lower immune function
Correlation indicates the direction and strength of association but does not establish causation.
Question 7: Power analysis is used in research planning primarily to:
- Determine the probability that the null hypothesis is true
- Estimate the required sample size to detect an effect of a given size (Correct answer)
- Control the Type I error rate
- Calculate the actual effect size after data collection
Correct answer: Estimate the required sample size to detect an effect of a given size
A priori power analysis uses expected effect size, alpha, and desired power (typically 0.80) to determine the minimum sample size needed.
BAPSY Psychological Research and Statistics 2
A researcher finds p = 0.03 with a small effect size (d = 0.15).
What is the most accurate interpretation?