Ia Experimental Study practice questions.

In an experimental study, state what the independent variable (IV) is.

• The variable that is measured as the outcome
• The variable that is deliberately manipulated by the researcher
• A variable that is held constant across conditions
• An uncontrolled variable that affects the results by chance

Answer: The variable that is deliberately manipulated by the researcher

The IV is the variable the experimenter manipulates or changes between conditions; the dependent variable is what is measured as the outcome.

A researcher wants to reduce order effects such as practice and fatigue in a repeated measures design. Suggest the most appropriate control.

• Random allocation of participants to conditions
• Counterbalancing the order of conditions
• Using a matched pairs design
• Standardising the instructions given to participants

Answer: Counterbalancing the order of conditions

Counterbalancing (e.g. ABBA) systematically varies the order of conditions across participants so that practice and fatigue effects are spread evenly and do not confound the IV.

Which statement is a null hypothesis?

• The IV will cause a significant increase in the DV
• There will be a difference between the two conditions
• Any difference is due to chance; the IV has no effect
• The results will support the theory being tested

Answer: Any difference is due to chance; the IV has no effect

The null hypothesis predicts no effect of the IV on the DV (any difference is due to chance); the research hypothesis predicts a genuine effect.

A study reports p = 0.03 using the conventional significance level of 0.05. Determine the correct conclusion.

• Retain the null hypothesis because the result occurred by chance
• Reject the null hypothesis as the result is significant
• The result proves the research hypothesis is true
• The sample size was too small to draw a conclusion

Answer: Reject the null hypothesis as the result is significant

Because p = 0.03 is below the 0.05 threshold, the probability the result is due to chance is acceptably low, so the null hypothesis is rejected. Significance does not 'prove' a hypothesis.

Which measure of central tendency is most appropriate to report when data are ordinal or contain extreme outliers?

• The mean
• The mode
• The median
• The standard deviation

Answer: The median

The median is not distorted by extreme scores and is appropriate for ordinal data, whereas the mean is pulled toward outliers and the standard deviation is a measure of dispersion, not central tendency.

A student uses an independent samples design to compare two groups on a rating scale (ordinal data). Determine the most appropriate inferential statistical test.

• Mann-Whitney U test
• Wilcoxon signed-ranks test
• Pearson's r correlation
• Chi-square test of association

Answer: Mann-Whitney U test

The Mann-Whitney U test compares two independent groups on ordinal data; Wilcoxon is for repeated measures, Pearson's r is for correlation, and chi-square is for nominal frequency data.