Flashcards in Practical terms Deck (19):
a measure of the closeness of agreement between an individual test result and the true value.
what does it mean if a test result is accurate?
it is in close agreement with the true value.
a value in a set of results that is judged not to be part of the inherent
a qualitative judgement expressing the extent to which a conclusion is justified by
the quality of the evidence.
Error (of measurement)
the difference between an individual measurement and the true value
(or accepted reference value) of the quantity being measured.
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.
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.
the precision obtained when measurement results are produced over a wider
timescale by different people using equivalent equipment in different (but equivalent) places.
the smallest change in the quantity being measured that can be detected by an instrument.
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.
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.
do not use this word - use repeatable, reproducible and confidence instead
apparatus with a graduated scale - uncertainty =
± half the smallest graduation.
apparatus with digital scale - uncertainty =
± the resolution of the
apparatus in each measurement.
percentage uncertainty = uncertainty/ quantity measured x 100%
why should the smallest measuring cylinder for the volume to be measured be used?
as this will have the lowest uncertainty
uncertainty with multiple measurements
e.g. burette/ measuring differences - there is an uncertainty with each measurement so use 2 x uncertainty in calculations
how should burette measurements be recorded?
to 2 d.p. with the last digit either 0 or 5.