# Frequently Asked Questions

- Why does the Visible Learning research use effect sizes?
- Why do you use an effect size of d=0.40 as a cut-off point and basically ignore effect sizes lower than 0.40?
- What is the preferred timescale over which an effect size can be calculated?
- Is there a bias when using effect sizes in favor of lower achieving students?
- What caution should I take when calculating an effect size?
- Why are effect sizes used when conducting meta-analysis?
- Why can an effect size of 0.40 be gained in a shorter timeframe?
- Can effect sizes be added (or averaged)?
- How accurate are the conclusions drawn from meta-analysis?
- How can the variability associated with each influence be evaluated?
- What type of effect size is appropriate?
- Why is the effect size of 0.4 seen as a ‘hinge point’?
- Should we only focus on influences with high effects sizes and leave out the low ones?
- How should research be grouped in meta-analyses?
- Is some research just too different to robustly average?
- Is it appropriate to rank effect sizes?
- Are meta-analyses truly as good as the original research?
- Is the use of effects sizes contingent on a normal distribution?
- Explain why confidence intervals were not used to help convey the effect size information.
- What should I keep in mind when interpreting meta-analyses?
- If the effect size of 1.33 for assessment-capable learners, indicates nearly four years of growth in a single year, would that mean that a 1st grader would be essentially learning at the grade level of a 5th grader by the end of first grade?
- Are you able to clarify how to interpret an effect size of 0.75 in relation to student learning?
- How do you place a numerical value on qualitative data collected?
- I have been told that .4 effect size represents one year’s growth in one year’s time. Is it really a proportional scale?
- For nearly 15 years you have carried out close to 1,200 meta-analyses on which factors are very influential on learning and which are not. Is it possible to apply your findings to all the schools regardless of any context and country?
- I tried to find what percentage of the data used in calculating the Visible Learning list effect size for feedback was from elementary, secondary, etc. Is that something you calculate and track?
- If you had to summarize your findings in one sentence, what would it be? Maybe: It is the teacher that makes the difference. What matters most is the teacher. Or something else?
- If we are talking about effect sizes based on student achievement, and if student achievement is measured through the flawed tools of standardized tests, then how accurate are these effect sizes?
- Why were you so interested in how people learn, that you did research on the things that have large influences on how teachers teach and wrote a whole book on it?
- How did you do your research to where you found out what different variables affect our learning the most?