Fig. 2

Changing prevalence of low back pain (filled squares and dotted line) and asymptomatic disc degeneration (filled diamonds and dashed line) with age. The filled squares represent the observed prevalence of low back pain among the Hungarian population (Horváth et al. 2010). The dotted line represents the result of curve fitting with the prevalence function \( {z}^{*}(t)=\alpha +\beta \left(1 - {e}^{-{\lambda}_1\left(t-{t}_0\right)}\right) \) (α = 0.031, β = 0.698, λ₁ = 0.0344, t ₀ = 13.3; R ² = 0.998). Filled diamonds are based on the graph (percentage of disc degeneration among asymptomatic women) of Powell et al. (1986). The prediction (dashed line) is based on the function \( {y}^{*}(t)=\frac{\left(1-\beta \right)\left(1 - {e}^{-{\lambda}_1\left(t-{t}_0\right)}\right)}{\ {e}^{-{\lambda}_1\left(t-{t}_0\right)}+\left(1-\beta \right)\left(1 - {e}^{-{\lambda}_1\left(t-{t}_0\right)}\right)} \) (R ² = 0.978). Note that the parameter values of y ^*(t) are taken from z ^*(t). The only adjustment made is to the symptom expression fraction β (normalized for a predefined duration factor μ; see main text for more details)