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