Meta-analysis and heterogeneity
9 important questions on Meta-analysis and heterogeneity
What are different types of heterogeneity
- Clinical heterogeneity/ diversity:
- Differences in clinical features of a study (patients, treatment, outcome)
- Methodological heterogeneity/diversity:
- Different study methodology (RCTs vs non RCTs)
- Statistical heterogeneity -> heterogeneity:
- Results from clinical/methodological (expected)
- Unknown (unexpected)
How do you address clinical and methodological heterogeneity/ diversity?
- Try to avoid it (expected heterogeneity)
- Adequate inclusion and exclusion criteria
- Define relevant subgroups a-priori
How do you identify statistical heterogeneity: unknown (unexpected)
- Common sense: eye-ball 'test'; overlapping Cls & identify source
- Test for homogeneity (Chi2) but type 2 error is likely
- Quantify heterogeneity (I2)
- Describe the % of the variability in effect estimates due to heterogeneity, not chance
- Value >50% sometimes labeled 'substantial'
- Higher grades + faster learning
- Never study anything twice
- 100% sure, 100% understanding
For my 1st exam I got a C. Then, I started looking for ways to learn better and I came across Study Smart. Since then I have scored a A+, A, A- and another A. I highly recommend it to everyone who wants to hear it. I am so happy with it!!
I was struggling to finish all my first-year subjects for 3 years. Then I discovered Study Smart, which helped me to finish all of them within 3 months.
Because of StudySmart, things are going well in many ways. Before, I always had study stress and no time for anything. Now I feel calm and confident (because of the program). I used to score a B, now I usually score an A or A+.
Hey Chris, I really want to thank you very much for developing the platform, I usually got around C for my exams, now I scored an A+, an A and a A- !!
Since using Study Smart, my average has increased significantly. I even completed a statistics course with a A+ while I'm bad at statistics. I took on extra courses this year, because of Study Smart. Thanks so much!
Ever since I started studying with StudySmart I passed all my exams !!! No more re-sits!! At first, I was happy with a pass and now I only get good grades. Many thanks!
I aced all the courses I studied with Study Smart. For law, I first scored a D, and now an A! I’m 100% sure that I’ll pass all the courses I study with Study Smart.
I always thought I studied well. My grades were fine. I could never have imagined that applying these study skills would have such a huge and direct impact on my grades, my speed and the pleasure I have in learning.
For the first time, I finally feel totally confident about the way I learn. I have the perfect overview and make great progress in terms of speed and the grades I get. Thanks, Chris!
I immediately started to enjoy learning again, and my grades soared. All of a sudden, everything went better. I highly recommend Study Smart to all students..
Being able to create my materials online made the process of studying so much smoother and quicker. I no longer have to spend a huge amount of my time on creating my summaries.
At first, my notes were a mess. Now I use Study Smart to take my notes in a perfectly structured way. It helps me to save a lot of time and do other things I enjoy.
Students that study with Study Smart get better grades. The system applies all the learning methods in such a way that both well-performing students and students who struggle perform much better.
Hi Chris, I would like to thank you very much. Last year I scored C on a course, and this year I got an A+ thanks to your method! Thank you very much!
The largest effect is that my child is more enthusiastic about school! Every parent wants their children to be happy at school, Study Smart made it happen.
In high school, I failed several exams, and that has really changed now. I actually needed this tool very much back then. Since I started studying with StudySmart, I haven't had any D's. My average score is now an A and those are results I would have never had in the past
With my old method, I passed only 3 out of 8 courses. Since I started taking my notes digitally in Study Smart, I have passed all my courses on the first try. For me, StudySmart takes away the stress of wondering if I will pass or not.
Thanks to StudySmart, I passed all my exams, and with better grades than before! On top of that, I have mastered a very good study method now, which I am confident will help me earn my degree.
How to address heterogeneity
- Check if data is entered correctly
- Choose to not do a meta-analysis: because the results are just too different
- Especially if they are inconsistent
- Explore heterogeneity
- Subgroup analyses
- Meta-regression
- Do this on pre-specified characteristics
- Ignore heterogeneity (NOT SMART TO DO)
- Change outcome (note: RD was heavily influenced by back ground risk = control group)
- Exclude studies (unwise, unless obvious reasons) (not because it is just an outlier)
- Perform a random effects meta-analysis (=incorporating heterogeneity)
When do you perform a random affects MA
- Lack of knowledge and then assumption: random
Random effects MA model involves an assumption that the effects of individual studies differ
How do you decide whether you do a random or a fixed effects in MA
- Decide before doing the meta-analyses: Whether the intervention effects are truly identical
- Fixed when this is likely
- Random when this is unlikely (mostly never truly identical)
- Others argue that fixed analysis can be used when there is heterogeneity and that it makes fewer assumptions than a random effects
- Lecturer: decide beforehand
How to interpret subgroups with caution
- Subgroups are observational
- Confounding by other trial-level characteristics
- Defined prior to study or post-hoc
- Multiple post-hoc tests: data dredging
- Is there clinical/ biological support
- Is the difference in effect worthwhile
- Between study comparisons not very reliable
- Because they are observational
How robust are the finings
- In every SR many, many decisions and assumptions need to be made
- What if different choices were made
- For this sensitivity analyses are used -> to make the different choices
Choices re:
- Methodological issues
- Inclusion criteria
- Different outcome measures in different studies
- Reanalyzing the data
- Imputing different (sensible) values for missing data
- Different statistical approaches
- Random instead of fixed effect model, or vv
What to use to report systematic reviews (sr)
The question on the page originate from the summary of the following study material:
- A unique study and practice tool
- Never study anything twice again
- Get the grades you hope for
- 100% sure, 100% understanding
