CAM201 Lecture Notes - Lecture 15: Managed Care, Internal Validity, Comorbidity
Experimental Studies
Studies of Treatment Effects
Experimental studies are studies in which the selection of treatment groups, nature of
interventions, management during follow-up, and measurement of outcomes are specified by
the investigator:
• Field trials: used to evaluate intervention intended to prevent disease in health people
(e.g. a field trial of a vaccine)
• Community trials: used to evaluate community-wide interventions (e.g. a community
trial of the effects of the fluoridation of public water supplies). Communities are
allocated and then matched to a control couity…
• Clinical trials: used to evaluate treatments for people who are ill (e.g. drug trials, new
surgical procedures, managed care interventions, lifestyle changes, et cetera).
Why and When are they done?
• Afford greater internal validity due to greater control and therefore offer greater
confidence and assurance regarding the truth of the results.
• Fastest and safest way to find treatments that work in people and ways to improve
health.
• Limitation: can be expensive.
• Can be done when randomisation is ethical when there is no compelling reason to
believe that either of the randomly allocated treatments is better than the other (if you
already know that one is better than the other it is unethical).
• Done when the primary outcome must be of benefit (i.e. a trial cannot be undertaken to
determine if one treatment is more harmful than another).
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These can happen all at that time-point, or there can be follow-up.
Sampling
Inclusion criteria:
• Patients must have the condition being studied.
• May be restricted to specific manifestations of the condition.
Exclusion criteria:
• Additional comorbidities other than the one being studied.
• Patients with contraindications to the treatment.
• Not expected to live long enough to experience the outcome of interest.
• Non-English speaking or refuse to participate.
Validity
• Internal Validity: the degree to which the results of the study are correct for the people
being studied. Determined by how methodologically sound the study is in reducing bias.
• External validity: the degree to which the results hold true in other settings, also called
geeralizaility. I.e. a I apply y suessful itervetio to people i the target
population and expect to get the same response?
How to deal with issues of external validity:
• Internal validity remains important with regard to ensuring the study sample fits the
research question.
• Avoid studying patients who are so unusual that experience with them generalises to
very few others.
• Simplify your trial: reformulate your study question and exclusion criteria to include
more participants (easier to recruit larger numbers of participants).
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