Technical Error of Measurement

Intra-observer TEM for two measurements, and inter-observer TEM involving two measurers

$$ TEM ~ = ~ \sqrt{\frac{\sum D ^ 2}{2N}} $$ where

D = The difference between measurements

N = The number of individuals measured

Inter-observer TEM with more than two observers

$$ TEM ~ = ~ \sqrt{\sum\nolimits_1 ^ N \left (\sum\nolimits_1 ^ K M ^ 2 ~ - ~ \frac{\left (\sum\nolimits_1 ^ K M \right ) ^ 2 / K}{N(K ~ - ~ 1)} \right )} $$ where

N = Number of subjects

K = Number of observers

M = Measurement

Relative TEM

$$ \% ~ TEM ~ = ~ \frac{TEM}{mean} ~ \times ~ 100 $$

Total TEM for two observers and two measurements per observer

$$ \text{Total TEM} ~ = ~ \sqrt{\frac{TEM ~ \times ~ (intra_1) ^ 2 ~ + ~ TEM ~ \times ~ (intra_2) ^ 2}{2} ~ + ~ TEM \times (inter) ^ 2} $$

Total TEM for three observers and two measurements per observer

$$ \text{Total TEM} ~ = ~ \sqrt{\frac{TEM ~ \times ~ (intra_1) ^ 2 ~ + ~ TEM ~ \times ~ (intra_2) ^ 2 ~ + ~ TEM ~ \times ~ (intra_3) ^ 2}{3} ~ + ~ TEM ~ \times ~ inter ^ 2} $$

Relative total TEM

$$ \% ~ \text{Total TEM} ~ = ~ \frac{\text{Total TEM}}{mean} ~ \times ~ 100 $$

Coefficient of Reliability (R)

$$ R ~ = ~ 1 ~ - ~ \frac{\text{Total TEM} ^ 2}{SD ^ 2} $$