Bland–Altman (method comparison)

Compare two measurement methods on the same items: bias (mean difference) and 95% limits of agreement.

Inputs

Result

Computed ✅

n (pairs): 8

Bias (mean diff): 0

SD(d): 1.4142

LoA: -2.7719 to 2.7719

Interpretation: If the limits of agreement are within your acceptable error range, the methods can be used interchangeably.

Step-by-step

Compute paired differences

Formula: d_i = B_i − A_i

Substitute: Compute d for each pair (n=8).

Result: First differences: -2, -1, 1, 1, 2, -1…
Compute bias (mean difference)

Formula: bias = mean(d) = (Σ d_i) / n

Substitute: bias = (Σ d_i)/8

Result: bias = 0
Compute SD of differences

Formula: SD(d) = sqrt( Σ(d_i − bias)^2 / (n−1) )

Substitute: n = 8

Result: SD(d) = 1.4142
Compute 95% limits of agreement

Formula: LoA = bias ± 1.96·SD(d)

Substitute: 0 ± 1.96·1.4142

Result: [-2.7719, 2.7719]