Lecture 29: Measuring Patients’ Experience Flashcards Preview

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1

Patient Reported Outcomes (PRO)

In certain cases, measuring health related quality of life is more appropriate than dichotomous outcomes regarding morbidity & mortality

give some examples?
when are they used?

– E.g., Rheumatoid arthritis (pain, function)
– E.g., Upper Respiratory Tract Infections (symptoms, function)
– E.g., Migraine (pain)
– E.g., Depression (mood)

– When the goal is to improve how people are feeling
– When life prolonging treatments lead to deterioration of HRQOL (e.g.,
cancer chemotherapy)
– When the relationship between lab measurements and HRQOL is
uncertain

2

2 types of Instruments Used to Measure Patient Reported Outcomes

generic

disease specific (see full list on slides)

3

what does St. George's Respiratory Questionnaire for

COPD (SGRQ-C) measure?

• Measure of health status for patients with COPD
• 40 items
• Score range 0-100
• Higher scores indicate worse health status

4

what are 2 measures of central tendency?

– Mean
– Median

5

what are 3 measures of spread?

– Standard deviation
– Range
– Interquartile range

6

clinical trials involve measurement at _________ and then compare the mean differences
between groups.

baseline and after treatment

Clinical trials may involve measurement of a continuous
outcome and then compare the mean scores between groups.

– Ignore the baseline data and just compare the mean post measurements
– Analyse the mean change in measurement from baseline to follow-up to
account for the influence of the baseline measurement
– Analyse the mean change in scores at follow-up whilst accounting for
baseline scores (achieved using a regression model, i.e., ANCOVA)

7

see slides for NSAIDS ex

ok

8

Statistical vs. Clinical Significance

• If something is statistically significant, it has no relevance to the clinical significance
– Very small differences that are not clinically meaningful may be statistically significant

• Statistical significance only means the results were unlikely due to random error

• Statistical Significance ≠ Clinical Significance

9

why is it easier to show statistically significant differences in a continuous variable than a dichotomous one

Why?
– Continuous variables are measured more “finely”
– It is easier to show differences in intervention and control on a scale
that has many points in comparison to one with rougher categories
(i.e., fewer points)

10

2 ways to interpret the results when the Units are Not Self Evident?

– Anchor
– Distribution based approaches

11

Anchor Based Approach

explain
what is MCID?

The anchor is an independent standard that is itself
interpretable and correlated to the instrument being explored

• Establish MCID (minimum clinical important difference)
– Smallest difference in score that patients perceive as beneficial and
would mandate an change in patients management

12

what are typical anchors?

• Typical anchor: no change, small change, moderate change, large change.

13

What do you Think is a Clinically Meaningful Improvement in SGRQ-C?

responder analysis:
**RATHER THAN LOOKING AT AVG CHANGE B/W GROUPS WE CANT AKE PROPORTION OF PPL THAT HAVE 4 PT CHANGE AND DEPICT THOSE NUMBERS AND COMPAR THE RESPONDERS IN YES NO DICHOTOMOUS WAY TO SEE IF THERE WAS A BENEFIT IN TREATMENT
Can talk about odds ratio, relative risk

Score Range (0 to 100)
A. 1 point
B. 5 points
C. 10 points
D. 20 points
E. 50 points
F. More than 50 points

Minimal Clinically Important Difference (MCID)
• MCID = 4 points as compared with the score with placebo

14

Distribution Based Approach

Effect Size
• Aka Standardized Mean Difference
• Summary estimate of effect expressed in Standard Deviation units

15

Standardized Mean Difference SMD equation

SMD = Mean (intervention) – Mean (control)
_________________________
Standard Deviation of Scores Measured at Baseline

Interpretation:

16

Interpretation of SMD values

– 0.5 means that the mean effect is half of an SD unit.
– Rule of Thumb: 0.2 Small Effect, 0.5 Moderate Effect, 0.8 Large Effect

17

only ______ can be entered in a contingency table

frequencies (i.e., dichotomous outcomes)

Other values (i.e., continuous outcomes) should not be cross
tabulated.
– Percentages
– Proportions
– Averages
– Ratios