The plethora of research literature available to the modern day biologists provides the luxury to conduct a unique procedure- an analysis of the meta(data of data).
GWAS- Genome Wide Association Studies find their utility in aiding the researcher narrowing down to a specific biomolecule, to target for any curative or vague analytical procedure for any particular trait.
To make meta-analysis realistic and closer to truth one needs to scrutinize every individual study on some benchmark, VENICE CRITERIA here comes in handy.
Venice criteria can be understood as a set of three scores which are used to grade the evidence produced by the study. Each of these three score can attain a maximum of ‘A’ grade, followed by ‘B’, and ‘C’ based on how meticulous the study was.
- The first score is generated for “Amount”
- Second scoring is done for “Replication” and
- And final score is awarded for “Protection from bias”.
When trying to elaborate on each of these three grading criteria one must play in numerical quantities, and the details of the same follow
- ‘A’ grade is awarded for large scale evidence
1000 subjects, case: control= 1:1, for least common genetic group
- For moderate evidence
100-1000 subjects, least common genetic group of interest
- For little evidence
less than 100 subjects, least common genetic group of interest
- Extensively replicated study supported by at least 1 well conducted meta-analysis.
- Well conducted meta-analysis which may have faced some methodological limitations, or the studies have moderate inconsistency.
- The analyte lacks association or independently replicated study, has a flawed meta-analysis and no between study consistencies.
Protection from bias
Biases in studies creep in from researchers’ preconceived notions, and affect the compilation of data and declaration of result, much like previous two conditions a study must also be scrutinized for biases that may have crept in.
- Biases are minimized still can affect the magnitude, but probably not the presence of association.
- Based on the amount of missing information on generation of evidence, but the bias doesn’t clearly defer any associations.
- Evidence for bias is so heavy that it may affect the existence of any association between studies.
Thus the grades may be scored as follows-
AAA– strong evidence
AAB, ABA, ABB, BAA, BBA, BBB, BAB– moderate evidence
Rest all scores will be treated as poor, unreliable evidence.
How to develop a search strategy for meta-analysis and systematic reviews?
It all begins with finding a topic to work on! Find yourself a topic which has current relevance and with publications of clinical trials, case-control or response-no response studies in recent years, Randomized control trials are the gold standard for such analyses and are also hard to find. The procedure emphasizes the studies being recent as that makes the data for analysis updated to the latest methods, techniques, and error minimization procedures. Also, the recentness of included studies empowers the analyst’s view of the relevance of the topic in current times.
To construct a systematic review and conduct a meta-analysis of all literature published on any topic, one must know how to precisely extract meta-data from varied databases at their disposal. One may create his corpus of experimental studies from any single database, say PubMed, by submitting a query containing words/phrases outlining names of a disorder, prescribed/ on trial drugs, and type of study expected all connected by use of operators. PubMed usually will return with results in five-figures and this is a fairly large dataset to sort out manually.
We must consider at this point that PubMed is not the ultimate collection of all the biological literature ever published and in current publications, it is a sufficiently well-informed database but mustn’t be regarded as complete. There are other databases which act as topic-specific databases and can be expected to contain a more concentrated literature on the theme they nurture.
Moving on to the actual development of query, the analyst must ascertain that the search string developed is complete in all respects, i.e. it contains all the MeSH terms for the items queried. Even though PubMed will automatically generate synonyms for a query from its database of MeSH terms in our experience we found providing the MeSH terms saw a steep fall in the number of results returned, the drop was so significant that previously obtained five-figured corpus was reduced to a measly three figured and was manually sortable.
It is noteworthy that if possible one mustn’t filter out studies published in languages other than English as it may make the study biased by eliminating participation of regional studies and data. The analyst may always try to contact the authors for the English version of the study and thus reduce the amount of bias, making the analysis robust.
For any query write to [email protected]
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