Epi Quiz 3
Data collection - treatment data
Assigned: treatment arm/group that the subject was allocated to (placebo or active) . Received: the actual treatment that the participant received
Alternatives to randomized trials (studies without comparison)
Case study: investigation of a single event of disease occurrence, Case series: investigation of a series of occurrence/treatments of the same or similar disease. Problem: no idea of exact relationship between intervention and outcome
Why do experimental studies?
Compare new drugs, treatments etc against current standard, evaluate effectiveness of prevention, assess the usefulness of programs for screening, evaluate impact of new policies
Type 1 error
Decide that treatments differ when in reality they do not
Type 2 error
Decide that treatments do not differ when in reality they do
Efficacy formula
Efficacy = (rate in control group - rate in treatment group)/rate in the control group
Selection of participants
Goal: study population is representative of reference population. Broad approach for recruitment is best
Alternatives to randomized trials (studies with comparison)
Historical controls: use as a comparison group with the disease from the past, Simultaneous Nonrandomized Controls: controls are selected in a nonrandomized fashion
NNT formula
NNT = 1/ (rate in control group - rate in treatment group)
Levels of masking
Participant (achieved through proper randomization and use of placebos), Allocators/data collectors, investigators/analysts, Double blinded (both participant and investigator are masked)
Masking
Procedures intended to keep participants in a study from knowing some facts or observations that might bias or influence their actions regarding the study. Basic intention: remove conscious or sub-conscious bias (prior to opinion) on the part of participants or investigators
Primary goal of randomization
Remove all subjective biases in the investigators and participants: investigators can't choose patients for tx, participants can't choose tx
Statistical power
ability of a test to detect differences in two treatments if a difference truly exists (1-beta)
Study Population
actual group of persons entered into the study (clinical trial)
Non-compliance
after randomization, participants may overtly or covertly not take the assigned treatment. Do not comply with their allocation. Regardless of this, data is analyzed by "intention to treat" not by what the actual treatment receipt was
Placebo Effect
any effect attributable to the expectation that the regimen will have an effect
Randomization
assignment of an individual or group to a treatment arm/study group by a means of chance. Normally by use of a random number table, computer generated random number pattern or other random generator (coin,dice, etc)
Loss to Follow-up
complete loss of contact, either through personal movement or death, that results in a participant not being able to be fully followed or treated
1 - beta
correct decision
Sample size
how many people must be included in a study to insure that there will be visible results, must choose appropriate size. Most vital component of trail
External validity
how well study pop can be applied to defined pop
Internal validity
how well was the study done
Added benefit of randomization
increase likelihood that study groups will be comparable (though not a guarantee of comparability)
Placebo
inert substance that looks, tastes, and smells like the agent being tested. Participants are unable to determine what treatment they are receiving
Stratification
layer the population to help improve comparability of study arms/groups. Will guarantee comparability for the stratified variables within the study arms/groups. (mostly done for age and gender)
too small sample size
lead to negative finding no matter the effectiveness of therapy
Data collection - outcome data
look for "improvement". Must also record any and all side effects
Data collection - prognostic variables
measure certain risk factors know to be prognosticators for a good or bad outcome. Must check that these variables are equally distributed after randomization
Efficacy
measure of the reduction in risk attributable to the treatment of interest
Number of patients who need to be treated (NNT)
number patients need to be treated to prevent one event. Assesses the impact on medical practice of the investigated treatment
Reference Population
overall society/population group that the study population will be selected from
too large sample size
overly cumbersome and financial burden
alpha
probability of making a type 1 error
beta
probability of making a type 2 error
Non-participation
problem with recruitment before randomization, may limit the ability to conduct the study
Results of controlled trials
survival curves/cumulative incidence, relative risk, # patients who need to be treated, efficacy, risk of death/incident event. Outcome rate in each group, may be the 'desired effect' or side effect. Often expressed in person years
Epi Objective for Clinical Trials
to evaluate both existing and new preventative and therapeutic measure and modes of health care delivery. "Does the treatment work?"
Old/current treatment
treatment, drug, existing behavior, or new health care system that we use as a comparison to the "new treatment". May be a placebo. Ethically: old treatment should be the best currently available treatment
Data collection in RCTs
treatment, outcome, prognostic profile at entry (criteria for outcome, data management, and acquisition must be explicit and written out)
Generalizability
ultimate goal of RCT: generalize results to general/reference pop