BAPSY - Bachelor of Arts in Psychology Bachelor of Arts in Psychology: Methodical & Stats Analysis 1 — Questions and Answers
Question 1: A researcher sets alpha at 0.05 and fails to reject a null hypothesis that is actually false. What type of error has occurred?
- Type I error
- Type II error (Correct answer)
- Sampling error
- Measurement error
Correct answer: Type II error
A Type II error (beta error) occurs when a researcher fails to reject a false null hypothesis — a 'miss.' A Type I error is the opposite: rejecting a true null hypothesis.
Question 2: A multiple regression model yields R² = 0.64. A researcher adds a second predictor and R² increases to 0.65. What should the researcher most likely conclude?
- The second predictor significantly improves the model
- The increase in R² is likely due to chance and the predictor adds little value (Correct answer)
- The model now explains 65% less variance
- Multicollinearity has been eliminated
Correct answer: The increase in R² is likely due to chance and the predictor adds little value
An R² increase of only 0.01 (1%) is trivially small. Researchers should examine adjusted R² and the predictor's significance before concluding the new variable meaningfully improves the model.
Question 3: Cohen's d is calculated as 0.20 for a study comparing two group means. How is this effect size conventionally interpreted?
- Large effect
- Medium effect
- Small effect (Correct answer)
- No effect
Correct answer: Small effect
By Cohen's conventions, d = 0.20 is a small effect, d = 0.50 is medium, and d = 0.80 or above is large. A small effect can still be meaningful depending on the research context.
Question 4: A psychologist measures anxiety levels in the same group of participants before therapy, after 4 weeks, and after 8 weeks. Which statistical test is most appropriate?
- Independent-samples t-test
- One-way between-subjects ANOVA
- Repeated-measures ANOVA (Correct answer)
- Chi-square goodness-of-fit test
Correct answer: Repeated-measures ANOVA
Repeated-measures ANOVA is used when the same participants are measured at three or more time points, accounting for within-subject correlation. An independent-samples t-test or between-subjects ANOVA would be inappropriate because the groups are not independent.
Question 5: A scale measuring depression produces very similar scores when administered to the same participants two weeks apart. This scale demonstrates high:
- Content validity
- Construct validity
- Test-retest reliability (Correct answer)
- Criterion validity
Correct answer: Test-retest reliability
Test-retest reliability refers to the consistency of scores over time when the measured construct has not changed. Validity addresses whether the scale measures what it is intended to measure — a separate property.
Question 6: In a normal distribution, approximately what percentage of scores fall within one standard deviation above and below the mean?
- 50%
- 68% (Correct answer)
- 95%
- 99.7%
Correct answer: 68%
The empirical rule states that approximately 68% of data fall within ±1 SD, 95% within ±2 SD, and 99.7% within ±3 SD of the mean in a normal distribution. This is foundational to interpreting z-scores and confidence intervals.
BAPSY - Bachelor of Arts in Psychology Bachelor of Arts in Psychology: Methodical & Stats Analysis 1
A researcher sets alpha at 0.05 and fails to reject a null hypothesis that is actually false.
What type of error has occurred?