CLS Research Methodology & Design 2 — Questions and Answers
Question 1: Which study design is most appropriate for establishing a causal relationship between laser treatment parameters and clinical outcomes?
- Case series
- Cross-sectional survey
- Randomized controlled trial (Correct answer)
- Retrospective chart review
Correct answer: Randomized controlled trial
Randomized controlled trials (RCTs) are the gold standard for establishing causation. Random assignment of participants to treatment and control groups eliminates selection bias and allows researchers to attribute outcome differences to the intervention.
Question 2: In a laser efficacy study, what is the primary purpose of a washout period between treatment phases in a crossover design?
- To increase sample size
- To allow carryover effects from the previous treatment to dissipate (Correct answer)
- To collect baseline measurements
- To train operators on the new protocol
Correct answer: To allow carryover effects from the previous treatment to dissipate
A washout period ensures that any residual effects from the first treatment phase have resolved before the participant crosses over to the next treatment. This prevents carryover effects from confounding comparisons between treatments.
Question 3: Which measurement scale is most appropriate for recording a patient's subjective pain level during laser treatment on a scale of 0 to 10?
- Nominal
- Ordinal
- Interval (Correct answer)
- Ratio
Correct answer: Interval
Pain scales like the Numeric Rating Scale (NRS 0–10) are treated as interval scales, where equal distances between numbers represent equal differences in pain intensity and a true zero indicates complete absence of pain, making ratio properties applicable as well.
Question 4: A laser study reports a p-value of 0.03. What does this indicate?
- There is a 3% chance the treatment is effective
- There is a 3% probability of observing results this extreme if the null hypothesis is true (Correct answer)
- The effect size is clinically significant
- 97% of participants responded to treatment
Correct answer: There is a 3% probability of observing results this extreme if the null hypothesis is true
A p-value of 0.03 means there is a 3% probability of obtaining the observed results (or more extreme) purely by chance if the null hypothesis (no effect) were true. It does not directly measure the probability that the treatment works or the size of the effect.
Question 5: What is blinding in the context of a laser treatment clinical trial?
- Restricting enrollment to patients with visual impairments
- Preventing participants and/or evaluators from knowing group assignment (Correct answer)
- Randomizing the order of laser pulse delivery
- Using opaque dressings over treated areas
Correct answer: Preventing participants and/or evaluators from knowing group assignment
Blinding (masking) prevents knowledge of group assignment (treatment vs. control) from influencing participant responses or evaluator assessments. Double-blinding, where both participants and outcome assessors are blinded, reduces bias most effectively.
Question 6: Which statistical test is most appropriate for comparing hair reduction percentages between three different laser wavelength groups?
- Paired t-test
- Chi-square test
- One-way ANOVA (Correct answer)
- Pearson correlation
Correct answer: One-way ANOVA
One-way ANOVA (Analysis of Variance) is used to compare means across three or more independent groups when the outcome variable is continuous. It tests whether at least one group mean differs significantly from the others.
CLS Research Methodology & Design 2
Which study design is most appropriate for establishing a causal relationship between laser treatment parameters and clinical outcomes?