Practical terms

Question 1

Accuracy

Answer 1

a measure of the closeness of agreement between an individual test result and the true value.

Question 2

what does it mean if a test result is accurate?

Answer 2

it is in close agreement with the true value.

Question 3

Anomaly (outlier)

Answer 3

a value in a set of results that is judged not to be part of the inherent
variation.

Question 4

Confidence

Answer 4

a qualitative judgement expressing the extent to which a conclusion is justified by
the quality of the evidence.

Question 5

Error (of measurement)

Answer 5

the difference between an individual measurement and the true value
(or accepted reference value) of the quantity being measured.

Question 6

Precision

Answer 6

the closeness of agreement between independent measurements obtained under the
same conditions. It depends only on the distribution of random errors (i.e. the spread of
measurements) and does not relate to the true value.

Question 7

Repeatability

Answer 7

the precision obtained when measurement results are produced over a short timescale by one person (or the same group) using the same equipment in the same place.

Question 8

Reproducibility

Answer 8

the precision obtained when measurement results are produced over a wider
timescale by different people using equivalent equipment in different (but equivalent) places.

Question 9

Resolution

Answer 9

the smallest change in the quantity being measured that can be detected by an instrument.

Question 10

Uncertainty

Answer 10

an estimate attached to a measurement which characterises the range of values within which the true value is asserted to lie. This is normally expressed as a range of values such as 44.0 ± 0.4.

Question 11

Validity

Answer 11

can apply to an individual measurement or a whole investigation. A measurement is valid
if it measures what it is supposed to be measuring. An investigative procedure is valid if it is suitable to answer the question being asked.

Question 12

reliable

Answer 12

do not use this word - use repeatable, reproducible and confidence instead

Question 13

apparatus with a graduated scale - uncertainty =

Answer 13

± half the smallest graduation.

Question 14

apparatus with digital scale - uncertainty =

Answer 14

± the resolution of the

apparatus in each measurement.

Question 15

percentage uncertainty

Answer 15

percentage uncertainty = uncertainty/ quantity measured x 100%

Question 16

why should the smallest measuring cylinder for the volume to be measured be used?

Answer 16

as this will have the lowest uncertainty

Question 17

uncertainty with multiple measurements

Answer 17

e.g. burette/ measuring differences - there is an uncertainty with each measurement so use 2 x uncertainty in calculations

Question 18

how should burette measurements be recorded?

Answer 18

to 2 d.p. with the last digit either 0 or 5.

Question 19

what is the uncertainty of a burette?

Answer 19

0.05 cm3 - this is half the smallest division of 0.1 cm3.