Fig 1.
Effect of random error on a Gaussian distribution.
Gaussian distribution curve illustrating how a random error in measurement will result in different proportions of data-points moving from one segment to another to increase the value of the standard deviation. The red line has a Standard deviation of 1.0. The dotted blue line has a standard deviation of 1.2. The grey areas show how the area in the centre of the curve has moved towards the tails thus increasing the areas below -2.0Z and above 2.0Z. Both distributions are Gaussian without generating moments of kurtosis or skewness. For explanation of the letters see the text.
Table 1.
The relative movement of points with distance from the mean.
Table 2.
Effect of imposed random error in weight on distribution of weight-for-height.
Fig 2.
Effect of imposed random error in weight on SD of the distribution of weight-for-height Z scores.
The error bars are 95% confidence intervals. All results use WHO2006 standards.
Fig 3.
Effect of imposed random error in weight on prevalence of global acute malnutrition (weight-for-height <-2 Z).
The error bars are 95% confidence intervals.
Fig 4.
Effect of imposed random error in weight on prevalence of severe acute malnutrition (weight-for-height <-3 Z).
The error bars are 95% confidence intervals.
Fig 5.
Change in the population mean Z-score from 50 simulated surveys with an initial mean of -0.6 Z, with imposed measurement errors in weight.
Error bars show 95% confidence intervals.
Fig 6.
Effect of random error in weight, with no error in height, on the Change in SD of the WHZ distribution from 6 simulated surveys each with different population mean WHZ–Z-scores.
The population mean WHZs were 0,-0.2,-0.4,-0.6,-0.8 and -1.0 Z.
Fig 7.
Effect of random error in weight, with no error in height, on the Change in GAM prevalence from 6 simulated surveys each with different population mean WHZ–Z-scores.
The population means were 0 (bottom dashed line),-0.2,-0.4,-0.6,-0.8 and -1.0 Z (top solid line).
Fig 8.
Effect of rounding/digit preference on the SD of WHZ distribution from 50 simulated surveys.
The terminal digit of the weights of the children were manipulated using the excel formula: round(weight/n)*n to 0.1Kg where n varied from 1 to 10. The error bars are the 95% confidence intervals.
Table 3.
Effect of rounding/digit preference of weight on the prevalence of GAM and SAM from 50 simulated surveys.
Table 4.
Effect of random error in measurement of height, age, weight and height together and MUAC on the assessment of malnutrition.
Fig 9.
The relationship between GAM and SAM in 9,399 surveys reported in the archival WHO global database on child growth and malnutrition (NCHS standards).
If the SD is 1.0 Z then all the surveys’ GAM/SAM ratios should lie upon the solid line, if the SD of the survey is between 0.8 Z and 1.2 Z then the data points should lie between the two dashed lines. Those surveys with points above the upper dashed line have an SD of greater than 1.2Z.
Fig 10.
The relationship between Global Stunting (<-2Z HAZ) and Severe Stunting (<-3HAZ) in 10,789 surveys reported in the archival WHO global database (NCHS standards).
If the SD is 1.0 Z then all the surveys’ global stunting/Severe stunting ratios should lie upon the solid line, if the SD of the survey is between 0.8 Z and 1.2 Z then the data points should lie between the two dashed lines. Those surveys with points above the upper dashed line have an SD of greater than 1.2Z.
Table 5.
Comparison of standard deviations from individual National surveys using different survey protocols from West African Countries.
Table 6.
The GAM and SAM from 100 West African Surveys computed with the average observed SDs and prevalence that would obtain if the SD had been either 1.0Z or 1.1Z.
Fig 11.
The percent of children with moderate malnutrition (<-2.0 Z) with a change in the SD of a survey, based upon a Gaussian distribution.
The mean Z of the distributions from top to bottom are -1.0 Z, -0.75 Z, -0.5 Z and -0.25 Z. The area representing an “acceptable” survey is given in light blue and a “good” survey in heavier blue.
Fig 12.
The percent of children with severe malnutrition (<-3.0 Z) with a change in the SD of a survey, based upon a Gaussian distribution.
The mean Z of the distributions from top to bottom are -1.0 Z, -0.75 Z, -0.5 Z and -0.25 Z. The area representing an “acceptable” survey is given in light blue and a “good” survey in heavier blue.