Duke Health - Module 5

Question 1

To determine validity we look at these criteria
* Was the sample of patients representative?
o The patient groups should be clearly defined and representative of the spectrum of disease found in most practices. Failure to clearly define the patients who entered the study increases the risk that the sample is —.
o To determine appropriateness of the sample, look for a clear description of … from the study. The — should be clearly specified along with the — used to diagnose patients with the disorder

Answer 1

unrepresentative
which patients were included and excluded
sampling methodology
objective criteria

Question 2

• Was follow-up sufficiently complete?
  o Prognostic factors are

Answer 2

characteristics of a particular patient that can be used to more accurately predict the course of a disease.

Question 3

o Example factors that may predict outcomes are:
(2)

Answer 3

 Demographic - age, gender, race, etc.
 Disease specific - e.g., stage of a tumor or disease

Question 4

o In comparing the prognosis of the 2 study groups, researchers should consider the …. Adjustments may be needed to determine if all relevant factors were considered. This requires clinical experience and/or knowledge of underlying biology.

Answer 4

similarity of the patients’ clinical characteristics

Question 5

• Were patients classified into prognostically homogenous groups?
  o Patients who are lost to follow-up may be

Answer 5

systematically different (such as higher or lower risk) from those who remain in the study and, if not accounted form could bias study results. Follow-up should be long enough to ensure all important outcomes are detected

Question 6

o How many patients lost to follow up is too many?

Answer 6

 80%

Question 7

• Were outcome criteria objective and unbiased?
  o Some outcomes are clearly defined, such as death or full recovery. Other outcomes may be less clearly defined
  o The same clear and unbiased criteria should be used to define outcomes and to evaluate patients
  o Outcome adjudicators should be

Answer 7

blinded to patient characteristics and prognostic factors to reduce bias

Question 8

Hazard ratios
(2)

Answer 8

• Measure how often a particular event happens in one group compared to how often it happens in another group, over time
• The way to summarize and analyze time-to-event data

Question 9

• HR =
  o 1:
  o >1 or <1:
  o 0.5:

Answer 9

there is no difference in survival between the two groups
the survival was better in one of the groups
a prognostic factor or intervention will cause the patient to progress less quickly to the primary endpoint proportionally to the comparator group

Question 10

Survival curves

Answer 10

• A curve that starts at 100% of the study population and shows the percentage of the population still surviving (or free of disease or some other outcome) at successive times for as long as information is available

Question 11

Survival curves
* A curve that starts at 100% of the study population and shows the percentage of the population still surviving (or free of disease or some other outcome) at successive times for as long as information is available
o For each interval, survival probability is calculated as the …
o This information is also captured below the survival curve; …

Answer 11

number of patients who have not experienced the event of interest divided by the number of patients at risk

at each interval, the number of patients at that point in time with the event-free survival are presented

Question 12

Prognostic result can be expressed in a few different ways:
(3)

Answer 12

• Absolute terms
• Relative terms
• Survival curves