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Non-monotonic dose-response curves
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Dose
response curves can come in several types.
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Linear,
in which a unit increase in the dose produces a unit increase in
the response. Linearity may be seen over a limited range of the
response curve.
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Non-linear,
in which the shape of the relationship is curved.
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There
are several types of non-linear relationships. Most non-linear curves
are assumed to be monotonic. In monotonic curves, the direction
of change does not reverse.
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The curve is either increasing (or flat) or decreasing (or flat)
across the full range of responses. It never increases then decreases.
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Sometimes
nonlinearity involves a threshold: beneath that level, there
is no response. |
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Recently
published results indicate that for endocrine disrupting chemicals,
at least under certain conditions, there may be no threshold.
In other words, any EDC contamination will change the response.
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Sometimes
nonlinearity involves an asymptote: once the dose reaches an asymptote,
no additional amount has an effect on the response.
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A
non-monotonic dose-response curve is by definition a type
of non-linear curve. |