Method comparison & Evaluation

Question 1

3 goals of lab dx.stics

Answer 1

• correct/appropriate test
• At the right time
• Performed accuratley

Question 2

whys is method comparison & evaluation important?

Answer 2

correct & timely dx for imporved/appropriate patient care

Question 3

when/hwat reasons would you evauluate/compare new methods

Answer 3

• current method unsatisfactory: in analytical (efficientcy); cost; reliability of suppliers/tech support; Safety
• new instrument
• new disease marker
• lab reorganisation

Question 4

what to consider during evaluation

Answer 4

• Analytical performance: which aspects; w/in run/ b/w run (if run on same day = get same results?)
• staffing
• sample vol
• cost

Question 5

important principles to successful evaluation of new method

Answer 5

• consider clinical PERSPECTIVE:
• Consider anlystical GOALS required
• Select analytical METHOD
• Conduct experiments/EVALUATION: compare w/ existing method
• Use stat.al tools & methodology to estimate diff b/w methods

Question 6

how to compare results b/w 2 methods?

Answer 6

• VISUAL: scatterplot, difference plot
• STAT.AL approaches: test diff. b/w means, regression analysis, correlation coeff. (R^2)
• CONTEXT: understand context when interpreting results

Question 7

2 types of total errors (innaccuracy)

Answer 7

• random error (imprecision)

- Systematic error (bias)

Question 8

4 cuases of systematic error

Answer 8

1. improperly prepped reagents
2. deterioration of reagents or calibrators
3. inappropriate storage of reagents / calibrators
4. variation in procedure b/w technologists

Question 9

4 Causes of random error

Answer 9

1. air bubbles in reagent
2. improperly mixed reagents
3. clogged or imprecise pipetter
4. improperly fitting pipette tips

Question 10

what is regression

Answer 10

• aka std error of estimate
• measures variability of observed values on regression line
• you want to minimise the distance b/w line & dots

Question 11

2 regression methods

Answer 11

• Deming regression: (not detect errors to method on X-axis)

- Passing-Bablock: less sensitive to outliers

Question 12

why is measurment uncertainty important?

Answer 12

• so we can tell if there’s been a significant change

Question 13

overall uncertainty (OU) equation

Answer 13

OU = √(MU^2 + BV^2)
MU^2 = variance of measurement uncertainty
BV^2 = variance of biological variation

Question 14

what is bland-altman analyses

Answer 14

• difference plot

- w/ difference on the y-axis

Question 15

T-test

Answer 15

• test for diff b/w means
• paired & unpaired t-test
• summarise overall bias (usually proportional)