GROUP 1 Adib Zubaidi Bin Rashid Mohd Amir Idhzuan Bin Johari Hamilah Binti Abd Ghani Lai Moon Ting.
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Transcript of GROUP 1 Adib Zubaidi Bin Rashid Mohd Amir Idhzuan Bin Johari Hamilah Binti Abd Ghani Lai Moon Ting.
GROUP 1GROUP 1
Adib Zubaidi Bin RashidMohd Amir Idhzuan Bin JohariHamilah Binti Abd GhaniLai Moon Ting
Precision & AccuracyPrecision & AccuracyDefinitionWays of describing precision
◦Deviation from mean◦Deviation from median◦Range◦Sample standard deviation (s)
Ways of describing accuracy◦Absolute errors◦Relative errors
DefinitionDefinitionPrecision
◦The closeness of results that have been obtained in exactly the same way
◦Generally, the precision of measurement is readily determined by simply repeating the measurement on replicate samples.
Accuracy◦The closeness of measurement to
the true or accepted value and is expressed by the errors.
◦Measures agreement between a result and the accepted value.
Ways of Describing Ways of Describing PrecisionPrecisionDeviation from mean
◦ The mean of two or more measurements is their average value.
◦ Deviation from mean is the differences between the values measured and the mean.
Deviation from median◦ The median is the middle value in a set of data
that have been arranged in numerical order.◦ Deviation from median is the differences
between the values measured and the median.
Range◦ Range is the difference between the highest
and the lowest values.
From Table 1.1, deviation from mean for each sample are:
di = | xt – x |A = 0.10%B = 0.09%C = 0.01%
di A= 24.39 – 24.28 = 0.10%
From Table 1.1, deviation from median for each sample are:
A = 0.11B = 0.08C = 0.00
Deviation from median for A= 24.39 – 24.28= 0.11
Ways of describing Ways of describing accuracyaccuracyAccuracy are expressed as:Absolute errorRelative error
Absolute error◦Equal to the difference between the
actual reading , xi, and the true (or accepted) value, xt.
EA = xi – xt
Example:From table 1.1, if analysis of chloride is
24.34%, calculate the absolute error.
Absolute error = 24.29% – 24.34% = –0.05%
Relative error◦Describes the error in relation to the
magnitude to the true value◦Normally described in terms of a
percentage of the true value, or in parts per thousand(ppt) of the true value.