Tag Archives: epidemiology

Historical cohorts: strengths and weaknesses

8 Jul

Historic cohort study, generally means to take a look back at events that already have taken place.


database (Photo credit: Sean MacEntee)

With the huge data bases containing Millions of lines of historic of several years of reimbursements of health care and health conditions now at the disposal of nation wide health care insurances like CNAMTS or RSI in France or Kaiser Permanente or Veteran Affairs in the USA , historical cohorts such as the one that is described in the article referenced below are very easy to implement provided that researchers have access to the data base and use the appropriate software to extract accurately the information to transform rough data in a relevant medical information. Personally I am a fan of SAS enterprise guide (no funding by SAS to disclose for this Blog).
But nothing being perfect in this world the weakness of such historical cohorts retrospectively rebuilt is that they can only put in evidence associations without absolutely no hint but the possible causation process involved in the association. Their force is of course the number of subjects analyzed (usually huge) and the provenance of the subjects (community and real life subjects as opposed as the carefully selected subjects of the controlled randomized trials).
But at the end of the day, to conclude like the study referenced below does, that high doses of ACE treatment causes a lowering of the mortality rate and the readmission rate is obviously going beyond the proper results of the study. Indeed no observational historic cohort, whatever the size of the analysed sample is, has the power to demonstrate a causality link. One possible explanation of the association unveiled by the study is that prescribers could be more reluctant to give high doses of ACE to the more fragile groups and comorbidity incurring groups of the studied population.

More content and referenced study:


Improved Outcomes in Heart Failure Treated With High-Dose ACE Inhibitors and ARBs: A Population-Based Study: full text research letter

Bad science (part two)

26 Nov
Cover of "Bad Science"

Cover of Bad Science

Look at this incredible video. The man who is talking is a medical practitioner who has become an epidemiologist. He belongs to a Cochrane group. The Cochrane groups chase false evidence-based medicine by reviewing all the published studies on a particular public health issue (like preventive behaviors, cancer screening, pharmaceutical industry lobbying and so on). It’s an awesome one man show made by a Doctor!


3 Sep

Wandering in the Hervé Maisonneuve Blog I just have learned that Daniel Schwartz passed on sept 6, 2009 at the age of 92.
If you were en ancient student of the « Certificat d’Etudes Statistiques Appliquées à la Médecine (CESAM) » like I was this name invariably must remember you the green book which you learned “by heart” and which made you shake with terror before exam. We, students, all named this green book “The Schwartz”. In those years (1992) I choose the Epidemiological option of the CESAM and succeeded the exam. What happened next is just history…

Legionella and Dengue are tracked by Facebook and google

20 Jun

In a precedent post I talked about Google correlate (see my post of 9 June).

Social networks and search engines are becoming the two new disease hunters of the 21 century.

Legionellosis epidemic has been elucidated in Los Angeles County by the mean of Facebook and dengue is being actually chased by Google.

In the next future you will perhaps start your next trip abroad by connecting you to Google Dengue Trends to get an instant indicator of Dengue activity in the World or to Health Map.

An interesting research article on neglected tropical disease surveillance has been published on the subject in Plos (Public Library of Science).


Get every new post delivered to your Inbox.

Join 82 other followers

%d bloggers like this: