Home » Topics » Nutrition and Anthropometry » Documentation on nutritional 'score' variable
| Re: Documentation on nutritional 'score' variable [message #2228 is a reply to message #2212] |
Fri, 30 May 2014 10:23   |
Liz-DHS
Messages: 1516
Registered: February 2013
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Senior Member |
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Dear User,
The Guide to DHS Statistics http://dhsprogram.com/publications/publication-dhsg1-dhs-que stionnaires-and-manuals.cfmcontains the following:
CHILDREN'S AND WOMEN'S NUTRITIONAL STATUS
CHILDREN'S NUTRITIONAL STATUS
Statistics: Percentages of Children Under 5 Years of Age, by Stunted, Wasted,
and Underweight
Definition
A. Coverage:
1. Population base: Living children born 0 to 59 months before the survey.
2. Time period: Current status at the time of the survey.
B. Numerators:
1. Severely stunted: Number of children whose height for age z-score is less than -3.0 standard
deviations (SD) below the mean on the NCHS/CDC/WHO international references standard.
2. Moderately stunted: Number of children whose height for age z-score is between 2.0 and
-2.99 standard deviations (SD) below the mean on the NCHS/CDC/WHO international
references standard.
3. Severely wasted: Number of children whose weight for height z-score is less than 3.0
standard deviations (SD) below the mean on the NCHS/CDC/WHO international references
standard.
4. Moderately wasted: Number of children whose weight for height z-score is between 2.0 and
2.99 standard deviations (SD) below the mean on the NCHS/CDC/WHO international
references standard.
5. Severely underweight: Number of children whose weight for age z-score is less than 2.0
standard deviations (SD) below the mean on the NCHS/CDC/WHO international references
standard.
6. Moderately underweight: Number of children whose weight for age z-score is between 2.0
and 2.99 standard deviations (SD) below the mean on the NCHS/CDC/WHO international
references standard.
C. Denominator: Number of living children between ages 0 and 59 months before the survey.
Calculation
A. The assignment of anthropmetric z-scores based on the NCHS/CDC/WHO International
Reference Standard is done through a complicated interpolation function that takes into account
sex, age (measured by difference in date of birth and date of interview, both precise to day of
month), height in centimeters, and weight in kilograms (precise to 100 grams). As part of a
creation of a recode file variables with the z-scores are calculated and included in that file. In the
process of assigning the z-scores, checks are made on their plausibility. Z-scores are assigned
missing to children with incomplete date of birth (month or year missing or "don't know"). The
reason is because z-scores are very sensitive to changes in age. Children with height for age
z-scores below 6 SD or above +6 SD, with weight for age z-scores below 6 SD or above +6
SD, or with weight for height z-scores below 4 SD or above +6 SD are flagged as having invalid
data. Also invalid are combinations of z-scores where height for age is less than 3.09 SD and
weight for age is more than +3.09 SD, or where height for age is more than +3.09 SD and weight
for age is less than 3.09 SD.
B. The percentages of children stunted, wasted, and underweight are equal to the specific numerators
divided by the denominators and multiplied by 100.
Handling of Missing Values
Children who were not weighed and measured and children whose values for weight and height were not
recorded are excluded from both the denominator and the numerators. Children whose day of month of
birth is missing or unknown are assigned day 15. Children who are flagged for out-of-range z-scores or
invalid z-scores are excluded from both the denominator and the numerators. Children with missing data
in the z-scores (date of birth incomplete or missing) are excluded from both the denominator and the
numerators.
Notes and Considerations
Stunting, based on a child's height and age, is a measure of chronic nutritional deficiency. Wasting, based
on a child's weight and height, is a measure of acute nutritional deficiency. Underweight, based on weight
and age, is a composite measure of both acute and chronic statuses. The NCHS/CDC/WHO standard is
based on well-nourished children in the United States. Due to natural variations in a well nourished
population, 2.2 percent of children will be between 2.0 and 2.99 SD below the mean, and 0.1 percent
will be 3.0 or more SD below the mean. The extent of malnutrition in a population should be taken by
the extent the proportions moderate and severe exceed these percentages that occur in a well-fed
population of children.
The NCHS/CDC/WHO international reference standard is a combination of two reference standards: one
for children under 24 months and the other for children 24216 months. The first standard, called the Fels
standard, is based on children whose height was taken while prone. The other standard, based on
NHANES data, is derived from children 24 months and older whose height was measured while they
were standing. For children 24 months of age or over, whose height was measured while lying down, one
centimeter should be subtracted from their measured height before calculating the z-scores.
Changes over Time
In phases of the DHS survey before phase IV (DHS+), only children of interviewed women and who
were under five years old (or the cutoff for the health section of the individual questionnaire) were
weighed and measured. In many surveys, only a subsample of these children were selected for
anthropometry. All comparisons between surveys, either over time or between countries, should take into
account the possible differences in the defined population base.
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