Study Results
A relative risk of ____ means there is no association between the risk factor and the disease
A relative risk of 1 means there is no difference in risk between the two groups
What does it mean when Relative Risk is 0.50
Negative association (Protective Effect). People with the risk factor are 0.5 times less likely to get the disease as people without the risk factor
Once Randomized, Always Analyze
Intention-to-treat Analysis (Primary analysis of a study should include patients as part of the group to which they were originally randomized)
In a study of former stroke patients, the time since the stoke for each patient was 1,1,2,2,3,5,13,13,39 and 66 months. What is the best average for these numbers?
The median
The median is usually preferred to other measures of central tendency when your data set is skewed
The major purpose of random assignment in a clinical trial is to:
Reduce selection bias in the allocation of treatment
Intervals where the true measure of association lies. They are used because there is not a way to calculate a true measure of association. This is a range around a point estimate.
Confidence Interval
A third factor that can be either positively or negatively associated with the intervention and outcome. This can distort a true association.
Confounding variable
A clinical trial looking at a new drug is studying the drug’s effect in a small number of healthy individuals
Phase I
A researcher finds a mean of 100 and a median of 50. What does this tell you about the shape of the distribution?
The distribution is skewed (to the right)
Subjects with the disease are more likely to recall the exposure of interest
Recall bias
A graphical display of estimated results from a number of scientific studies addressing the same question, along with the overall results. The vertical line of this graph is the null hypothesis. What type of graph is this?
Forest plots
_______trials determine whether an intervention produces the expected result under ideal circumstances, whereas Effectiveness trials measure the degree of beneficial effect under “real world” clinical settings
Efficacy trials determine whether an intervention produces the expected result under ideal circumstances
A clinical trial looking at a small number of patients with the disease of interest. Assess treatment efficacy, optimal dosing and adverse effects
Phase II
The term that gives an idea of how far data points are from the mean… a measure of how spread out numbers are. Its symbol is σ (sigma) and it is the square root of the Variance.
The standard deviation
Subjects alter their behavior when they know they are being studied
Hawthorne Effect, a type of measurement bias (information is gathered in a way that distorts the truth)
This is portrayed at the bottom of a forest plot and shows the result when all the individual studies are combined together and averaged. The shape shows the limits of the 95% confidence intervals.
The diamond of a forest plot
A study design in which a researcher measures exposure and disease simultaneously
Cross-sectional study
The purpose of double blinding in a clinical trial is to:
Avoid observer and subject bias
The difference between the 25th and 75th percentiles of a data set.
The interquartile range,
equal to Q3 minus Q1
Patients with severe disease are less likely to be studied, because they die
Late-look bias
A meta-analysis is done to see if ordering diagnostic tests reduces patient anxiety. In the forest plot of the odds ratio for reduced anxiety, the 95% confidence interval of each study crosses 1.00 and the diamond crosses 1.00. What is a correct interpretation of the results?
The study did not observe a statistically significant difference between the treatment and control groups.
If the individual study crosses the vertical line, it means the null value lies within the 95% confidence interval.
The ability to generalize your study results to the population at large
External Validity
An independent group of experts who monitor patient safety and treatment efficacy data while a clinical trial is ongoing.
Data Safety Monitoring Board (DSMB) or Data Monitoring Committee (DMC)
Routine method of displaying time-to-event (survival) data by treatment group. This is a common figure seen in clinical trials.
Kaplan Meier plot: routine method of displaying time-to-event (survival) data by treatment group. The event may be death, a non-fatal event (e.g. disease recurrence), a composite outcome (e.g. time to death, myocardial infarction or stroke whichever occurs first) or occasionally a good outcome (e.g. time to recovery)
Investigator inadvertently conveys his high expectations to subjects, who then produce the expected result
Pygmalion effect