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Calculating Standard Deviations (S.D.) or Z-score by Hand
Survey date = 17 March 1997 (170397)
| Case | District | HHID | Child ID | DOB | Age | Sex | Weight | WAZ |
| 1 | 1 | 1 | 1 | 170396 | F | 9.1 | ||
| 2 | 1 | 1 | 2 | 170996 | F | 6.5 | ||
| 3 | 1 | 2 | 1 | 121295 | F | 11.9 | ||
| 4 | 1 | 3 | 1 | 010297 | M | 3.9 |
Calculate age: March 17, 1997 - March 17, 1996 = 12 months
Find Median weight for 12 month
old girls from the reference chart below:
9.5 kgs (The correct cell in the reference chart below is colored
pink.)
Calculate the difference between
the median weight for 12 month old girls
and the child's weight (found in the chart above): 9.1 - 9.5 = -0.4
(Notice
that you should always put the child's actual weight first in the subtraction.)
Note that the child's weight falls below the median for her age group, between the median and -1 standard deviations. (The -1 standard deviation cell is colored blue in the reference chart below.)
Subtract "median value" minus "-1 standard deviation value" to calculate one standard deviation: 9.5 - 8.5 = 1.0
To calculate the weight-for-age z-score, divide the child's "deviation" from the median (calculated in step 3) by the standard deviation (calculated in step 5): -0.4/1.0 = - 0.40 (Notice that because the child's weight was below the median, the weight-for-age z-score is negative.)
Exercise
Use steps 1-6 above to calculate the weight-for-age z-scores for Cases 2 and 3. You can use the same reference chart for them. However, if you were to have a boy for a case, you would need to use a separate chart for boys. Both cases below are girls, therefore you can reference the chart provided to perform the exercise.
After you finish you can check your answers:
CASE 2 Girl: Birthdate: Sept. 28, 1994
Interview date: Nov.19, 1996 Weight (kg): 11.1
CASE 3 Girl: Birthdate: Dec. 12, 1995
Interview date: Nov. 19, 1996 Weight (kg): 9.8
Table 24. WEIGHT (KG) BY AGE OF GIRLS AGED 0-36 MONTHS |
||||||||||||||||||||||
Age |
CENTILES |
STANDARD DEVIATIONS |
Age |
|||||||||||||||||||
Months |
3rd | 5th | 10th | 20th | 30th | 40th | 50th | 60th | 70th | 80th | 90th | 95th | 97th | -3 S.D. | -2 S.D. | -1 S.D. | Median | +1 S.D. | +2 S.D. | +3 S.D. | Months |
|
0 |
2.3 |
2.4 |
2.6 |
2.8 |
3.0 |
3.1 |
3.2 |
3.3 |
3.4 |
3.5 |
3.7 |
3.8 |
3.9 |
1.8 |
2.2 |
2.7 |
3.2 |
3.6 |
4.0 |
4.3 |
0 |
|
1 |
2.9 |
3.0 |
3.2 |
3.5 |
3.7 |
3.8 |
4.0 |
4.1 |
4.3 |
4.4 |
4.7 |
4.9 |
5.0 |
2.2 |
2.8 |
3.4 |
4.0 |
4.5 |
5.1 |
5.6 |
1 |
|
2 |
3.4 |
3.6 |
3.8 |
4.1 |
4.4 |
4.5 |
4.7 |
4.9 |
5.1 |
5.3 |
5.6 |
5.8 |
6.0 |
2.7 |
3.3 |
4.0 |
4.7 |
5.4 |
6.1 |
6.7 |
2 |
|
3 |
4.0 |
4.2 |
4.4 |
4.8 |
5.0 |
5.2 |
5.4 |
5.6 |
5.8 |
6.1 |
6.4 |
6.7 |
6.9 |
3.2 |
3.9 |
4.7 |
5.4 |
6.2 |
7.0 |
7.7 |
3 |
|
4 |
4.6 |
4.7 |
5.0 |
5.4 |
5.6 |
5.8 |
6.0 |
6.3 |
6.5 |
6.8 |
7.1 |
7.4 |
7.6 |
3.7 |
4.5 |
5.3 |
6.0 |
6.9 |
7.7 |
8.6 |
4 |
|
5 |
5.1 |
5.3 |
5.6 |
6.0 |
6.2 |
6.4 |
6.7 |
6.9 |
7.1 |
7.4 |
7.8 |
8.1 |
8.3 |
4.1 |
5.0 |
5.8 |
6.7 |
7.5 |
8.4 |
9.3 |
5 |
|
6 |
5.6 |
5.8 |
6.1 |
6.5 |
6.8 |
7.0 |
7.2 |
7.4 |
7.7 |
8.0 |
8.4 |
8.7 |
8.9 |
4.6 |
5.5 |
6.3 |
7.2 |
8.1 |
9.0 |
10.0 |
6 |
|
7 |
6.0 |
6.2 |
6.5 |
6.9 |
7.2 |
7.5 |
7.7 |
7.9 |
8.2 |
8.5 |
8.9 |
9.3 |
9.5 |
5.0 |
5.9 |
6.8 |
7.7 |
8.7 |
9.6 |
10.5 |
7 |
|
8 |
6.4 |
6.6 |
7.0 |
7.4 |
7.7 |
7.9 |
8.2 |
8.4 |
8.7 |
9.0 |
9.4 |
9.8 |
10.0 |
5.3 |
6.3 |
7.2 |
8.2 |
9.1 |
10.1 |
11.1 |
8 |
|
9 |
6.7 |
7.0 |
7.3 |
7.7 |
8.1 |
8.3 |
8.6 |
8.8 |
9.1 |
9.4 |
9.8 |
10.0 |
10.4 |
5.7 |
6.6 |
7.6 |
8.6 |
9.6 |
10.5 |
11.5 |
9 |
|
10 |
7.0 |
7.3 |
7.6 |
8.1 |
8.4 |
8.7 |
8.9 |
9.2 |
9.4 |
9.8 |
10.2 |
10.4 |
10.8 |
5.9 |
6.9 |
7.9 |
8.9 |
9.9 |
10.9 |
11.9 |
10 |
|
11 |
7.3 |
7.6 |
7.9 |
8.4 |
8.7 |
9.0 |
9.2 |
9.5 |
9.8 |
10.1 |
10.6 |
10.8 |
11.2 |
6.2 |
7.2 |
8.2 |
9.2 |
10.3 |
11.3 |
12.3 |
11 |
|
12 |
7.6 |
7.8 |
8.2 |
8.6 |
9.0 |
9.3 |
9.5 |
9.8 |
10.1 |
10.4 |
10.9 |
11.2 |
11.5 |
6.4 |
7.4 |
8.5 |
9.5 |
10.6 |
11.6 |
12.7 |
12 |
|
13 |
7.8 |
8.0 |
8.4 |
8.9 |
9.2 |
9.5 |
9.8 |
10.1 |
10.3 |
10.7 |
11.1 |
11.5 |
11.8 |
6.6 |
7.6 |
8.7 |
9.8 |
10.8 |
11.9 |
13.0 |
13 |
|
14 |
8.0 |
8.2 |
8.6 |
9.1 |
9.5 |
9.8 |
10.0 |
10.3 |
10.6 |
10.9 |
11.4 |
11.8 |
12.0 |
6.7 |
7.8 |
8.9 |
10.0 |
11.1 |
12.2 |
13.2 |
14 |
|
15 |
8.1 |
8.4 |
8.8 |
9.3 |
9.7 |
10.0 |
10.2 |
10.5 |
10.8 |
11.2 |
11.6 |
12.0 |
12.3 |
6.9 |
8.0 |
9.1 |
10.2 |
11.3 |
12.4 |
13.5 |
15 |
|
16 |
8.3 |
8.6 |
9.0 |
9.5 |
9.9 |
10.2 |
10.4 |
10.7 |
11.0 |
11.4 |
11.9 |
12.3 |
12.5 |
7.0 |
8.2 |
9.3 |
10.4 |
11.5 |
12.6 |
13.7 |
16 |
|
17 |
8.5 |
8.7 |
9.2 |
9.7 |
10.0 |
10.3 |
10.6 |
10.9 |
11.2 |
11.6 |
12.1 |
12.5 |
12.7 |
7.2 |
8.3 |
9.5 |
10.6 |
11.8 |
12.9 |
14.0 |
17 |
|
18 |
8.6 |
8.9 |
9.3 |
9.8 |
10.2 |
10.5 |
10.8 |
11.1 |
11.4 |
11.8 |
12.3 |
12.7 |
13.0 |
7.3 |
8.5 |
9.7 |
10.8 |
12.0 |
13.1 |
14.2 |
18 |
|
19 |
8.8 |
9.1 |
9.5 |
10.0 |
10.4 |
10.7 |
11.0 |
11.3 |
11.6 |
12.0 |
12.5 |
12.9 |
13.2 |
7.5 |
8.6 |
9.8 |
11.0 |
12.2 |
13.3 |
14.5 |
19 |
|
20 |
8.9 |
9.2 |
9.7 |
10.2 |
10.6 |
10.9 |
11.2 |
11.5 |
11.8 |
12.2 |
12.7 |
13.1 |
13.4 |
7.6 |
8.8 |
10.0 |
11.2 |
12.4 |
13.5 |
14.7 |
20 |
|
21 |
9.1 |
9.4 |
9.8 |
10.4 |
10.7 |
11.1 |
11.4 |
11.7 |
12.0 |
12.4 |
12.9 |
13.3 |
13.6 |
7.7 |
9.0 |
10.2 |
11.4 |
12.6 |
13.8 |
15.0 |
21 |
|
22 |
9.3 |
9.5 |
10.0 |
10.5 |
10.9 |
11.2 |
11.5 |
11.9 |
12.2 |
12.6 |
13.1 |
13.6 |
13.9 |
7.9 |
9.1 |
10.3 |
11.5 |
12.8 |
14.0 |
15.2 |
22 |
|
23 |
9.4 |
9.7 |
10.2 |
10.7 |
11.1 |
11.4 |
11.7 |
12.0 |
12.4 |
12.8 |
13.3 |
13.8 |
14.1 |
8.0 |
9.3 |
10.5 |
11.7 |
13.0 |
14.2 |
15.5 |
23 |
|
24 |
9.6 |
9.9 |
10.3 |
10.9 |
11.3 |
11.6 |
11.9 |
12.2 |
12.6 |
13.0 |
13.6 |
14.0 |
14.3 |
8.2 |
9.4 |
10.7 |
11.9 |
13.2 |
14.5 |
15.8 |
24 |
|
25 |
9.7 |
10.0 |
10.5 |
11.0 |
11.4 |
11.8 |
12.1 |
12.4 |
12.8 |
13.2 |
13.8 |
14.2 |
14.6 |
8.3 |
9.6 |
10.8 |
12.1 |
13.4 |
14.7 |
16.0 |
25 |
|
26 |
9.9 |
10.2 |
10.6 |
11.2 |
11.6 |
11.9 |
12.3 |
12.6 |
13.0 |
13.4 |
14.0 |
14.5 |
14.8 |
8.5 |
9.7 |
11.0 |
12.3 |
13.6 |
14.9 |
16.3 |
26 |
|
27 |
10.1 |
10.3 |
10.8 |
11.4 |
11.8 |
12.1 |
12.4 |
12.8 |
13.1 |
13.6 |
14.2 |
14.7 |
15.0 |
8.6 |
9.9 |
11.2 |
12.4 |
13.8 |
15.2 |
16.6 |
27 |
|
28 |
10.2 |
10.5 |
11.0 |
11.5 |
11.9 |
12.3 |
12.6 |
13.0 |
13.3 |
13.8 |
14.4 |
14.9 |
15.2 |
8.8 |
10.1 |
11.3 |
12.6 |
14.0 |
15.4 |
16.8 |
28 |
|
29 |
10.4 |
10.7 |
11.1 |
11.7 |
12.1 |
12.4 |
12.8 |
13.1 |
13.5 |
14.0 |
14.6 |
15.1 |
15.5 |
8.9 |
10.2 |
11.5 |
12.8 |
14.2 |
15.6 |
17.1 |
29 |
|
30 |
10.5 |
10.8 |
11.3 |
11.8 |
12.3 |
12.6 |
12.9 |
13.3 |
13.7 |
14.2 |
14.8 |
15.3 |
15.7 |
9.1 |
10.3 |
11.6 |
12.9 |
14.4 |
15.9 |
17.3 |
30 |
|
31 |
10.6 |
11.0 |
11.4 |
12.0 |
12.4 |
12.8 |
13.1 |
13.5 |
13.9 |
14.4 |
15.0 |
15.6 |
15.9 |
9.2 |
10.5 |
11.8 |
13.1 |
14.6 |
16.1 |
17.6 |
31 |
|
32 |
10.8 |
11.1 |
11.6 |
12.2 |
12.6 |
12.9 |
13.3 |
13.7 |
14.1 |
14.6 |
15.2 |
15.8 |
16.1 |
9.3 |
10.6 |
11.9 |
13.3 |
14.8 |
16.3 |
17.8 |
32 |
|
33 |
10.9 |
11.2 |
11.7 |
12.3 |
12.7 |
13.1 |
13.4 |
13.8 |
14.2 |
14.7 |
15.4 |
16.0 |
16.3 |
9.4 |
10.7 |
12.1 |
13.4 |
15.0 |
16.5 |
18.1 |
33 |
|
34 |
11.0 |
11.4 |
11.9 |
12.5 |
12.9 |
13.3 |
13.6 |
14.0 |
14.4 |
14.9 |
15.6 |
16.2 |
16.6 |
9.5 |
10.9 |
12.2 |
13.6 |
15.2 |
16.7 |
18.3 |
34 |
|
35 |
11.2 |
11.5 |
12.0 |
12.6 |
13.0 |
13.4 |
13.8 |
14.2 |
14.6 |
15.1 |
15.8 |
16.4 |
16.8 |
9.6 |
11.0 |
12.4 |
13.8 |
15.4 |
16.9 |
18.5 |
35 |
|
36 |
11.3 |
11.6 |
12.1 |
12.7 |
13.2 |
13.6 |
13.9 |
14.3 |
14.8 |
15.3 |
16.0 |
16.6 |
17.0 |
9.7 |
11.1 |
12.5 |
13.9 |
15.5 |
17.1 |
18.8 |
36 |
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