epi Flashcards
Statistical Associations
generally, positive findings of epidemiologic or clinical outcome studies
Perfect Linear relationship
For every unit of increase in one variable, the other variable increases
or decreases proportionally & Coefficient, represented by r
Intra-class correlation
Looks at the agreement of measurements within classes or categories & Is
a useful measure of validity, reliability, or inter-rater agreement
The fewer the subjects, the more likely results may be influenced by
chance sampling variation
selection bias
study subjects are selected in a way that can increase or decrease magnitude of an
association—misleadingly
Information bias
when the method of data collection makes the information obtained from two or
more groups differ in some misleading way. Result in misclassification of subjects with respect to
disease or possible causal factors
specification
simplest method for controlling variables in the data analysis & data from each
Sensitivity deals with
true positives
specificity deals with
false positives
If the query is new and there is not much information on what is to be investigated, you should
start with a
case study, if it doesn’t, next step would be look at case series
Quasi-experimental Designs have many features of an RCT, but
generally are not double blinded
and if single group, there is no randomization
RCT
Should be randomized, blinded (2 way preferred), no other bias in structure or in execution
of trial, and appropriate analysis
Journal editors must be more cautious about making sure that
replication—an essential issue in
research reliability—can be done
Credit for the modern randomized trial is usually given to
Sir Austin Bradford Hill
RCT are not appropriate for
cancer screening
Efficacy refers to
an RCT or 2 group or more trial of some other type; maintain research rigor here
Effectiveness
refers to a single group trial where pre and post intervention is evaluated; similar to
daily practice
phase 1
are usually conducted after the safety of the new intervention has been
documented in animal research, and their purpose is to document the safety of the intervention in
humans – usually case series or outcome studies
phase 2
the intervention is given to a small group of real patients, and the purpose of this study is
to evaluate the efficacy of different modes of administration of the intervention to patients – focus on efficacy while still providing information on safety
phase 3
Performed after a given procedure has been shown to be safe with a reasonable chance of improving patients’ conditions. Most phase 3 trials are randomized controlled trials - Here the study would be looking at two or more groups with persons assigned to different interventions/placebo
phase 4
Studies are equivalent to post-marketing studies of the intervention; they are performed to identify and monitor possible adverse events not yet documented - Earlier studies, even RCTs, do not give an opportunity to discover whether a product will produce a side effect in someone with an esoteric condition. This phase is quite important
parallel design
Most randomized controlled trials have parallel designs in which each group of participants is exposed to only one of the study interventions
crossover design
crossover design refers to a study in which each of the participants is given all of the study interventions in successive periods. The order in which the participants receive each of the study interventions is determined at random
factorial design
A randomized controlled trial has a factorial design when two or more experimental interventions are not only evaluated separately but also against each other and against a control - A 2 × 2 factorial design generates four sets of data to analyze: data on patients who received none of the interventions, patients who received treatment A, patients who received treatment B, and patients who received both A and B
sequential trial
A sequential trial is a study with parallel design in which the number of participants is not specified by the investigators beforehand. Instead, the investigators continue recruiting participants until a clear benefit of one of the interventions is observed or until they become convinced that there are no important differences between the interventions
fixed trials
Alternatively, in a fixed trial, the investigators establish deductively the number of participants (sample size) that will be studied. This number can be decided arbitrarily or can be calculated using statistical methods. The latter is a more commonly used method.
statistical correction (intent to treat)
A method to correct for differential dropout rates between patients from one arm of the study and another is to analyze data by the intent to treat—that is, data are analyzed in the way patients were randomized, regardless of whether or not they received the intended intervention. The intent to treat correction is a form of protection against bias and is believed to strengthen the conclusions of a study
