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The benefits of a
crossover design are substantial. Both interventions (hypertonic
and isotonic saline) are applied to each individual, so that each
forms its own control, making the "treatment" and "control"
group identical except for the order and time. By applying a washout
period, it is assumed that all measurements taken after the washout
are no longer affected by the previous intervention,
allowing the subject to return to the "natural" baseline
state before the next condition is initiated. If problems with
washout are observed, the investigator has to increase the time
between repeated measures. For details regarding crossover designs,
see Chapter 6.
| Figure
19.1: Cross-over Design
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