Transcript (accuracy) dan ketelitian (precision)

1). Rata-rata (mean) dan standar deviasi (deviation)
2). Ketepatan (accuracy) dan ketelitian (precision)
Rata-rata (mean)
The mean, X, is the numerical average obtained by dividing the sum
of the individual measurements by the number of measurements
Table Berat Uang Koin
What is the mean for the data in Table above?
Answer:
3.080 + 3.094 + 3.107 + 3.056 + 3.112 + 3.174 + 3.198 = 21.821
Standard Deviation)
The absolute standard deviation, s, describes the spread of
individual measurements about the mean
Relative Standard Deviation
X 100%
Table Berat Uang Koin
What are the standard deviation, the relative standard
deviation, and the percent relative standard deviation for the
data in Table above ?
Hasil pengukuran berat
koin bisa dituliskan sbb:
Berat koin = 3.117±0.051g
Accuracy and Precision
Much of science has to do with the
collection and manipulation of quantitative
or numerical data.
 The value of computations using numerical
data is greatly dependent on the accuracy
and precision of that data.

Accuracy and Precision
Conceptual illustration
Accuracy and Precision
Conceptual illustration
Accuracy and Precision
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Accuracy and precision can not be considered
independently
A number can be accurate and not precise
A number can be precise and not accurate
A number can be precise and accurate
ACCURACY
Accuracy can be defined as how close a
number is to what it should be.
 Accuracy is determined by comparing a
number to a known or accepted value.
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Assessing Accuracy
PRECISION
Precision: The closeness of agreement between independent test
results obtained under stipulated conditions
􀂾 repeatability: precision under similar conditions
􀂾 reproducibility: precision under different conditions
Assessing Precision
Measurement of precision for a data set is the standard deviation (s)
For data sets that have more than 20 points
For data sets < 20 points
Relative Standard Deviation
X 100%
Example 1:

How old are you?
 I am 22 years old (1)
 I am 22 years and 8 months old (2)
 I am 22 years, 8 months, and 5 days old
(3)
 I am 22 years, 8 months, 5 days, and 10
hours old (4)
Accuracy vs. Precision for
Example 1
Statement (2) is more accurate and more
precise that statement (1).
 Statement (3) is more accurate and more
precise than statement (2).
 Statement (4) is more accurate and more
precise than statement (3).
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Example 2:

How long is a string ?
 Student A measures the string at 2.63 ±
0.02 m.
 Using the same ruler, Student B
measures the string at 1.98 ± 0.01 m.
 Who is most precise?
 Who is most accurate?
Accuracy vs. Precision for
Example 2
The actual measurement is 2.65 m.
 Student A is fairly accurate and also very
precise.
 Student B is very precise, however, he is
not very accurate. The lack of accuracy is
due to using the ruler incorrectly.
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Example 3
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Using a centigram balance,
 Student A measured a sample at 3 ±0 g.
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Student B measured the same sample at
3.00 ±0.01 g.
Who is most precise?
Who is most accurate?
Accuracy vs. Precision for
Example 3
The actual measurement is 3.01 g.
 Student A is reasonably accurate. He/She
was not very precise because the balance
was not capable of measuring to two
decimal places.
 Student B is much more accurate because of
the precision of his/her measurement and
closeness of her value to the actual value.
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