Exam Two - Observational (prognostic) studies

Question 1

prognosis relates to ….

Answer 1

• evaluation of the timecourse for a disease
• potential influence of exposure to various factors

Question 2

prognosis in PT is used to…

Answer 2

• identify the risk of developing a future problem
• predict the ultimate outcomes of impairments or functional limitations

Question 3

prognosis is often evaluated using observational study designs such as…

Answer 3

• prospective cohort
• retrospective cohort
• case control

Question 4

T or F: statistics used in prognostic studies are also common in experimental studies with categorical outcomes

Answer 4

T

Question 5

Relative risk definition

Answer 5

• the likelihood that someone who has been exposed to a factor will develop the outcome of interest
• cumulative over an entire study, using a defined endpoint (only use beginning and end, nothing in the middle!)

Question 6

how to calculate RR?

Answer 6

top box has yes/no condition left side has if they were exposed or not. (label a,b,c,d)
rr = (a/(a+b))/(c/(c+d))

Question 7

how to interpret RR?

Answer 7

<1 = decreased likelihood
>1 = increased likelihood
=1 = no prognostic value

Question 8

how much does exposure matter?

Answer 8

rr (increase or reduction) = |(1-rr)| x 100

Question 9

when is rr statistically significant?

Answer 9

when confidence intervals do not contain one

Question 10

hazard ratios

Answer 10

• represent instantaneous risk during the study time period
• better for indicating risks that happen at any time during the study interval
• know that this is different than RR!

Question 11

hazard ratios and survival cues, what is it?

Answer 11

“survival cues” represent the percentage of each group surviving versus time

Question 12

_________ is concerned with the total events over time while _________ is concerned with likelihood of events at any time.

Answer 12

relative risk
hazard ratio

Question 13

Odds ratio

Answer 13

odds of experiencing an exposure among people with and without the outcome
- retrospective estimate of relative risk
- commonly used in retrospective cohort studies or case control studies

Question 14

how to calculate odds ratio

Answer 14

cross multiply the box
- only useful when one factor is assessed, if multiple factors then you should use logistic regression

Question 15

odds ratio answers the question of:

Answer 15

is it more likely to find an exposure among people with the outcome

Question 16

T or F: odds ratio uses the same interpretation as relative risk

Answer 16

true
<1 = decreased likelihood
>1 = increased likelihood
=1 = no prognostic value

Question 17

What factors should you consider when looking at prognosis study quality?

Answer 17

enrollment
follow up
measurement of outcome and blinding
outcome reporting

Question 18

what are some questions you should be concerned about when analyzing prognosis study quality

Answer 18

• was the cohort assembled at a common point in their course of disease?
• was patient follow up sufficiently long?
• was patient follow up complete?
• how objective is the outcome?
• results reporting?

Question 19

why should you be concerned if the cohort was assembled at a common point in the course of their disease?

Answer 19

• best if enrolled at a uniform early time in the disease - called inception cohort
• limited survivor bias (good outcomes over-represented because more advanced disease associated with poorer prognosis)

Question 20

why should you be concerned if the patient follow up was sufficiently long?

Answer 20

• length of time needs to be long enough to detect the outcome of interest and this varies depending on the outcome

Question 21

why should you care if patient follow up is complete?

Answer 21

• because you don’t want high drop out rates
• if people do drop out, you need to explain why

Question 22

why should you care about how objective the outcome is?

Answer 22

• how is variable operationally defined
• are results open to interpretation
• were results determined by rates who are masked to prognostic factors?

Question 23

why should we care about how results are reported?

Answer 23

• survival curves and hazard ratios are preferred/better/more contemporary
• RR or odds ratios only give beginning and ending values