From: samia Alhabib <[log in to unmask]>
Subject:
To: [log in to unmask]
Received: Friday, May 10, 2013, 12:55 AM

thank you all for your feedback. we got only 2 RCT ans and4 prospective cohort and one retrospective study. I guess one cannot combine 2 RCT , we need at least to have more than 3 studies to combine them?

The studies are similar in terms of outcomes,  stage of disease, and measurements, but differ of course in some aspects such as race, gender...  So, I understand from your comments that metanalysis is inappropriate and narrative one is the option?

Best Regards,

Samia

Dr. Samia Alhabib, MD, PhD

Sent from Samsung Mobile

-------- Original message --------
From: "Dr. Carlos Cuello" <[log in to unmask]>
Date:
To: [log in to unmask]
Subject:

Hi Samia

I agree with Tom that both designs should not be combined. This great question drives us to another question

If you have a body of evidence from RCTs, why would you need the observational studies?

 

I would say that depends on the outcome, and you need to decide a priori which outcomes will you be evaluating; 

For example, if you need to evaluate whether your intervention provoques a rare adverse event (let's say, pancytopenia), then perhaps the cohort studies (or other observational designs) will be more useful than the RCTs.

RCTs by default are considered high quality evidence that you can downgrade depending on certain criteria (see GRADE methods). Furthermore, observational studies are considered low quality evidence that can also be upgraded depending on the GRADE criteria (very similar to the Hills criteria, actually). My suggestion is that you could add GRADE SoF tables to your work.

best

On Thu, May 9, 2013 at 12:55 AM, Tom Jefferson <[log in to unmask]> wrote:

Samia, I strongly advise you to keep RCTs and cohorts separate, you canot combine their results as they two different designs. Are the cohorts all prospective? If not you should further subdivide them, if they are comparative that is.

Good luck with interpreting the observational studies, especially if they tell you a different story from the RCTs.

Best wishes,

Tom.

On 9 May 2013 02:41, Paul Elias <[log in to unmask]> wrote:

I would not combine them in a meta analysis if this is the first q..you should not combine controlled studies with uncontrolled studies.....I would combine the RCTs and observational designs separately and discuss them as such. If you did combine (though I argue no), I would then do a sensitivity type analysis and separate the observationals from the full set (7????) to show the impact on the summary estimate etc.            Best, Paul E. Alexander   --- On Wed, 5/8/13, Mohamed El Shayeb <[log in to unmask]> wrote: From: Mohamed El Shayeb <[log in to unmask]> Subject: To: [log in to unmask] Received: Wednesday, May 8, 2013, 11:05 PM Hi Samia, In my humble opinion, there are two notions in this. First, and most important, the conceptual notion. This should be determined by the researcher's discretion. I think the questions that really count rather than just the design will be: Do the studies measure the same clinical end point? Are the results overall consistent in regards to the overall effect magnitude and direction? Are patients characteristics somehow similar across the studies? The second notion is the statistical notion of heterogeneity. There is no arbitrary line or threshold for heterogeneity that you may consider for such a decision. Further, the presence or absence of heterogeneity will then dictate which model to use (random versus mixed effects model). The first assumes similar distribution among all the studies. The latter assumes that each individual study distribution is part of a bigger distribution for the combined effect and does the calculation accordingly. In an article that I think someone in the list distributed few weeks ago (unfortunately can't remember who and when) the issue of dealing with heterogeneity in reviews was discussed. No criticism was directed to the presence or absence of heterogeneity itself. In fact, the article criticized usage of an inappropriate model, and emphasized the importance of addressing and quantifying heterogeneity (Q and I2 statistics); interpreting it if you can and use the proper model. I will try to find the article and send it to you. I hope this is helpful for you and your team . Cheers, Mohamed El Shayeb Health Technology and Policy Unit University of Alberta 3025 Research Transition Facility 8308 114 street Edmonton, Alberta, Canada T6G2V2 Tel: +1 (780) 248 1524 On Wed, May 8, 2013 at 10:05 AM, samia Alhabib <[log in to unmask]">[log in to unmask]> wrote: Dear list;  we are doing systematic review of the effectiveness of DC beads and conventional chemotherapy in treating hepatocellular carcinoma, and we found only 2 RCTs and 5 cohort studies that fulfill our inclusion criteria. My Q: is it appropriate to combine these studies although of different designs? bear in mind that it is uncommon disease. .. Another Q that we debated with the research team; what is the level of heterogeneity that could be acceptable to combine the effect  size? Appreciate your feedback Samia Dr. Samia Alhabib, MD, PhD Sent from Samsung Mobile

--
Dr Tom Jefferson
www.attentiallebufale.it

--
Carlos A. Cuello-García, MD
Centre for Evidence Based Practice & Knowledge Translation 

Tecnológico de Monterrey School of Medicine & Health Sciences

Cochrane Mexican Branch · Iberoamerican Cochrane Centre

Editorial Board, The Journal of Pediatrics

CITES piso 3. Morones Prieto 3000 pte. Col. Doctores 64710 

Monterrey, NL. Mexico. 

☎ +52.81.8888.2223 & 2154. Skype: dr.carlos.cuello

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