Z score

Dr. Arindam Sarkar
Department of Geography
Purash Kanpur Haridas Nandi College
arindam.srkr1@gmail.com
Z-Score
Or
Standard Score
Dr. Arindam Sarkar , Department of Geography
Purash Kanpur Haridas Nandi College Website: https://pkhnm.ac.in/
Email ID: arindam.srkr1@gmail.com

 Z Score is also called as Standard Score
 It provide idea about how far from the mean a data point
is located
 It is a technical measures of how many standard deviation
located below or above the population mean of a data set
 Z Score is placed on a normal distribution curve
 Z Score ranges from (-3 S.D ) up to ( +3 S.D )
 ( -3 S.D )would fall into the extreme left of the normal
distribution curve and as well as
 ( +3 S.D )would be located at the extreme right of the
normal distribution curve
 For calculation it is essential to know the population mean
and standard deviation of population
 Technically a Z score is the value of SD from the population
mean Value

 Z Score 1 means 1 standard deviation above the mean.
 Z Score 2 stands for 2 standard deviation above the mean.
 Z score (-1.7) indicate (-1.7) SD below the mean.
 Actually this type of phenomena are associated with the
normal distribution curve.
 Z score value of 0 indicate about the value that is exactly
average.
 Z score of +3 indicate that the value much higher than the
mean and located far from the mean center.
 The value of z score in the center of the normal
distribution curve is obvious.
 Any Z score value located right of the mean are positive
and left of the mean are negative.

Calculation Procedure
1. Calculate total population ( ∑x ).
2. Calculate Population Mean .
3. Calculate ( x – mean ) . Difference of population from mean.
4. Calculate the value of ( x – mean )².
5. Calculate SD value of population.
SD =
6. Calculation Z Score value =
N
xx  2
)(
SD
xx
Zx
)( 


Mapping Procedure
1. Representation of SC Population is most suitable
through Choropleth mapping.
2. Z score value may be appear (-) and (+) both.
3. That is why you need to prepare a index in corporate
the whole (+) and (-) value.
4. In same sequence where ‘0’ is located in the mid of the
context.
5. Representation of choropleth is done by continues line
for (+) value and discontinues line for (-) value located.
6. Color of the line (continues or discontinues ) would be
Red.

Data And Calculation Table For Z Score
SL No. Name of Police % 0f SC
Population (x)
(x –Mean) (x – Mean)² Z x = (x – Mean)²/SD
1 Bally 5.35 -12.434 154.601 -1.659
2 Lilua 29.48 11.696 136.800 1.560
3 Howrah MC 4.40 -3.384 179.127 -1.785
4 Domjur 21.11 3.326 11.063 0.444
5 Sankrail 26.24 8.456 71.507 1.128
6 Panchla 18.92 1.136 1.291 0.152
7 Jagathballabpur 21.00 3.216 10.344 0.429
8 Udaynarayanpur 18.07 0.286 0.082 0.038
9 Amta 24.26 6.476 41.941 0.864
10 Bagnan 12.68 -5.104 26.049 -0.681
11 Uluberia 24.17 6.386 40.783 0.852
12 Bauria 10.96 -6.824 46.565 -0.910
13 Shyampur 14.55 -3.234 10.458 -0.431
Total 231.19 730.611

Calculation of Mean = =
= 17.78
Calculation of SD = =
= 7.496
Sample Calculation Of Z Score For Bally :
Z Score
=-1.659
N
xx  2
)(
N
x 13
19.231
13
)611.73019.231( 
SD
xx
Zx
)(
)(


496.7
)434.12(


Interpretation
In whole howrah district 8 C.D Blocks are under
grater than mean (+ value) and 5 C>D Block is
under less than mean value (- value).The ‘0’
value of Z Score divides whole district into two
region.(+) z score value are located in the amta
,uluberiya ,pancla, sankrail,
jagatballavpur,udaynarayanpur,domjur and
lilua (highest) C.D Block. (-) z score value are
located in the bally,howrah MC,bagnana and
syampur C.D Block.

Z score

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