Accuracy & precision

Question 1

Define measurement error

Answer 1

refers to the difference between the true value & the measured value

Question 2

What can cause a variation in measurement?

Answer 2

1. People: skillset, confidence, experience
2. Equipment: calibration, model’s
3. The process: method of measurement
4. The object itself

Question 3

Describe normal distribution

Answer 3

ND is represented by a bell-shaped curve in which the central point indicates most likely where the true value lies

The spread/width of the curve indicates the variability/uncertainty in measurements

The standard deviation shows you the distribution of measurements, 95% confidence in true value, 5% room for error

A small SD curve indicates less uncertainty, a large SD curve indicates more uncertainty

Question 4

Define uncertainty

Answer 4

The range of values in which we think the true value lies

Question 5

Define accuracy

Answer 5

The closeness in agreement with the ‘true’ value, e.g., hitting the bullseye

Question 6

Define precision

Answer 6

The closeness in agreement between independent measurements under similar conditions, how close the repeated measurements are to each other
e.g., Darts on a dart board all clustered together even if not near bullseye

Question 7

Define repeatability

Answer 7

Involves variation in measurements taken by a single person or instrument on the same patient in the same conditions
- same observer used
- same location
- same instrument used
- same measurement procedure
Measurements are taken in a short period of time e.g., for NIBP every 5 minutes

Question 8

Define reproducibility

Answer 8

The ability of a study or investigation to be entirely reproduced either by the researcher or someone else independently
Involves the use of different people, their level of education/ skillset must be similar
Equipment must be calibrated

Question 9

Describe the effect of poor accuracy & precision on patient care (NIBP)

Answer 9

1. Impact diagnosis: the patient may be misdiagnosed, or disease is missed
2. It can influence treatment decisions, as unreliable data may lead to inappropriate therapy (over/under treatment)
3. Data will not be reproducible, leading to invalid conclusions

Question 10

Describe sources of error in the context of NIBP

Answer 10

1. Observer error: reading at different angles, poor technique & rounding differences
2. Equipment error: poor calibration, worn sensors
3. Subject error: patient moves
4. Environmental error: changes in humidity, temperature, noise etc