A study is called an observational study when exposure status (e.g. on drug A or drug B or no drug) is observed (measured) by the investigator whereas in a randomised trial the investigator organises for participants to be randomised to drug A or drug B or perhaps a placebo.
In the observational study example, a clinician unassociated with the study has usually prescribed drug A or drug B to participants as part of usual care and all the study investigator does is ‘observe’ / measure what drugs the participants are taking. The investigator in an observational study has no say what drugs the participants take.
The word ‘controlled’ in randomised controlled trials simply refers to the fact that participants are randomly allocated to the study intervention or to a comparison or ‘control’ group. A control group is actually common in both observational studies and RCTs, but in RCTs participants are allocated to groups at random.
Cheers Rod Jackson
> On 26/01/2020, at 12:15 PM, Moacyr Roberto Cuce Nobre <[log in to unmask]> wrote:
>
> I do not understand Observational Study as a no controlled study. Some
> people are exposed and some are not.
> _______________________________________
> Moacyr Roberto Cuce Nobre, MD, MS, PhD
> Equipe de Epidemiologia Clínica e Apoio à Pesquisa
> Instituto do Coração (InCor) Hospital das Clínicas
> Faculdade de Medicina da Universidade de São Paulo
> 55 11 2661 5941 (fone/fax)
> 55 11 991 331 009 (celular)
>
>
>> Em qui., 23 de jan. de 2020 às 07:51, Tom Jefferson
>> <[log in to unmask]> escreveu:
>> Dear EBMers, thank you to all those who responded to my to questions. I have collated the answers verbatim whenever I could. They are summarised in a table which I will send to interested requestors.
>> I have a few comments and would be grateful if you could add to them.
>> What strikes me is the heterogeneous nature of the answers.
>> I used 2 vague terms "trial" and "clinical trial" and purposely did not mention terms like "controlled", "placebo", "randomised" and few respondents did.
>> Despite their vagueness, the terms are in everyday use and I believe their definitions should be tigthened.
>> Alarm bells started going off in my head when I saw case series and even retrospective cohort studies referred to as "trials". One of the biggest culprits in this mess is, alas, clinicaltrials.gov. People who are planning to conduct and report case series register them and then seemingly feel entitled to call them "trials" as the register bears that name.
>> The whole terminology needs tightening up to avoid misrepresentation and the usual reporting bias creeping in.
>> To me a trial is an experiment, a clinical trial is an experiment on humans only, then there may be randomisation, blinding etc but these should be described as features further refining the design.
>> All trials are controlled (conducted) by investigators to an extent, with randomisation being one extreme.
>> Case series are what comes through the surgery door either in all cases or particular types of cases.
>> Observational studies have no control (conduction) exerted.
>> I hope you find this discussion interesting.
>> Tom.
>> Dr Tom Jefferson
>> Senior Associate Tutor, University of Oxford
>> Researcher, Nordic Cochrane Centre
>> Visiting Professor, Newcastle University
>> ** Announcing the RIAT Support Center: free support & $150,000 grant competition **
>> ** Details at https://restoringtrials.org/ **
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