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http://www.isakonline.com/

Nikki Brown

Errors in Anthropometry Errors in anthropometry can affect:

Precision

Accuracy

Validity

3 major sources of error are significant:

1. Measurement error

2. Alterations in composition and physical properties of certain tissues

3. Use of invalid assumptions in derivation of BC from anthropometric measures

Measurement Error Random Error – limit precision or extent to which

repeat measures give same value

Can derive from examiner error:

Inadequate training

Instrument error

Difficulties in making measurement

Approaches to minimise random error:

Training

Standardised techniques

Using precise, correctly calibrated instruments

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Measurement Error Systematic Error – affect accuracy or degree to which

measurement depart from true values

Most common form results from equipment bias

Example:

2 people take SF measure on same person but use different calipers with different compressions

Timing of measures

Example:

ST growth study – progressive decrease in height though day – compromise accuracy

Anthropometric measurement never known with absolute certainty

Precision We can also establish precision (and accuracy) of

measurement technique prior to use

Poor precision reflects:

Within-examiner error

Between-examiner error – surveys with multiple

examiners?

How do we assess precision?

Technical Error Measurement (TEM)

% Technical error (%TEM)

Coefficient of reliability

TEM Gives error margin of a trait and is

therefore an accuracy index

Inter-tester or Intra-tester

Where D is the difference between the 2 measurements, and N is the sample size

Relative TEM (%TEM)

Provides estimation of error

magnitude relative to size of the

measure

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TEM Where D is the difference between the 2

measurements, and N is the sample size

Relative TEM (%)

Task – Intra TEM

Subject 1 Subject2 Subject 3 Subject 4 Subject 5

1st measurement 7.0 9.3 6.0 13.6 11.2

2nd measurement 9.2 8.8 6.2 12.4 10.0

Results of bicep skinfold taken by same anthropometrist in 5

subjects

Using the sheet provided calculate:

Intra technical error of measurement

Relative TEM (%)

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Task – Inter TEM

Subject 1 Subject2 Subject 3 Subject 4 Subject 5

1st measurer 16.0 14.6 15.0 14.0 22.6

2nd measurer 18.2 20.8 12.8 14.4 16.8

Results of abdominal skinfold taken by two different

antrhopometrists in 5 subjects

Using the sheet provided calculate:

Inter technical error of measurement

Relative TEM (%)

Interpretation and Application

of TEMs Example 1:

An athlete is measured and is found to have a triceps skinfold of

9.3mm. The anthropometrists TEM is 0.33mm. What are the

confidence limits for that athlete?

In general the TEM is the standard error of a single measure.

An approximate 68% confidence interval (1SE) for the true

value will be from:

[9.3 – 0.33] to [9.3 + 0.33] i.e. from 9.0mm to 9.6mm]

An approximate 95% confidence interval (2SE) for the true

value will be from:

[9.3 – 2(0.33)] to [9.3 + 2(0.33)] i.e. from 8.6mm to 10.0mm

Interpretation and Application

of TEMs Example 2:

An elite gymnast has her ∑7 skinfolds measured two weeks apart to monitor

her body composition (38mm and 41mm). The anthropometrist obtained a

TEM of 2.9mm.

The coach is keen for all gymnasts ∑7 to be below 40mm. Having observed

41mm at the 2nd time of measurement can the coach conclude that the true

value of ∑7 exceeded 41mm at the time of the measurement?

An approximate 95% confidence interval (2SE) for the true value will be

from:

[-41 – 2(0.29)] to [41 + 2(0.29)] i.e. from 35 mm to 47 mm]

Since 40 is within the interval it would be concluded (at the 2.5%

significance level) that the true value did not exceed 40mm.

Sig is 2.5%, rather than 5% because the test carries out is one-sided

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Summary

All body composition techniques have limitations

Anthropometric measurement never known with

absolute certainty

In order to use anthropometric data effectively must

be aware of measurement error

Inter-tester

Intra-tester

Relative TEM (%)