F 2 ¼
Number of failed tests
Total number of tests
 100
ð3:4Þ
F 3 can be calculated as follows: the number of times by which an individual
concentration is greater than (or less than, when the objective is minimum). The
objective is termed “excursion”, then; when the test value not exceed the objective,
excursion can be influenced by Eq. (3.5), while when test value not fall below the
objective, Eq. (3.6) can be performed:
excursion i ¼
Failed test value i
Objective i
À 1
ð3:5Þ
excursion i ¼
Objective i
Failed test value i
À 1
ð3:6Þ
The collective amount by which individual tests are out of compliance can be
calculated by summing the excursions of individual tests from their objectives and
dividing the total number of tests (both those meeting objectives and those not
meeting objectives). This variable, referred to as the normalized sum of excursions,
or nse, can be calculated as:
nse ¼
P n
i¼1 excursion i
total number of tests
ð3:7Þ
F 3 is then calculated by an asymptotic function that scales the normalized sum of
the excursions from
objectives (nse) to yield a range between 0 and 100.
F 3 ¼
nse
0:01nse þ 0:01
ð3:8Þ
Criteria
Indices
Pesce and Wunderlin
Liou
NSF WQI
CCME WQI
ISQA
Good
Fair
Bad
Parameters measured using continuous sampling
Adaptability to different uses of water body
Existing guidelines to define objectives
Experience of real application
Consideration of the amplitude
(amount by which the objectives are not met)
Programming difficulty
Tolerance to missing data
Need of synchronized data
Tolerance to wrong data
Fig. 3.2 Comparison of WQI with different criteria [11]
86
H. A. Aziz et al.
Number of failed tests
Total number of tests
 100
ð3:4Þ
F 3 can be calculated as follows: the number of times by which an individual
concentration is greater than (or less than, when the objective is minimum). The
objective is termed “excursion”, then; when the test value not exceed the objective,
excursion can be influenced by Eq. (3.5), while when test value not fall below the
objective, Eq. (3.6) can be performed:
excursion i ¼
Failed test value i
Objective i
À 1
ð3:5Þ
excursion i ¼
Objective i
Failed test value i
À 1
ð3:6Þ
The collective amount by which individual tests are out of compliance can be
calculated by summing the excursions of individual tests from their objectives and
dividing the total number of tests (both those meeting objectives and those not
meeting objectives). This variable, referred to as the normalized sum of excursions,
or nse, can be calculated as:
nse ¼
P n
i¼1 excursion i
total number of tests
ð3:7Þ
F 3 is then calculated by an asymptotic function that scales the normalized sum of
the excursions from
objectives (nse) to yield a range between 0 and 100.
F 3 ¼
nse
0:01nse þ 0:01
ð3:8Þ
Criteria
Indices
Pesce and Wunderlin
Liou
NSF WQI
CCME WQI
ISQA
Good
Fair
Bad
Parameters measured using continuous sampling
Adaptability to different uses of water body
Existing guidelines to define objectives
Experience of real application
Consideration of the amplitude
(amount by which the objectives are not met)
Programming difficulty
Tolerance to missing data
Need of synchronized data
Tolerance to wrong data
Fig. 3.2 Comparison of WQI with different criteria [11]
86
H. A. Aziz et al.