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Do double-blind studies with informed consent yield externally valid results? An empirical test
1Department of Psychology, University of Connecticut, Storrs 06269-1020.
Psychopharmacology
|January 1, 1993
Summary
Caffeine increases alertness and blood pressure, but only when participants know they are consuming it. This challenges the validity of typical double-blind studies in real-world settings.
Area of Science:
- Psychopharmacology
- Human Physiology
Background:
- Caffeine is a widely consumed psychoactive substance.
- The impact of participant expectations on caffeine's effects is not fully understood.
- Double-blind studies are common but may not reflect real-world conditions.
Purpose of the Study:
- To investigate the subjective and physiological effects of caffeine.
- To examine the independent and interactive effects of instructions, actual beverage content, and time on caffeine's impact.
- To assess the external validity of typical double-blind studies.
Main Methods:
- A 3x2x3 factorial design was employed.
- Independent variables included instructions (told caffeine, told no caffeine, not told), actual beverage content (caffeine, no caffeine), and time after ingestion (15, 30, 45 min).
- Subjective and physiological measures were recorded.
Main Results:
- Instructions influenced alertness at 15 minutes.
- Caffeine ingestion increased alertness at 30 minutes and systolic blood pressure at 30 and 45 minutes.
- A significant interaction between instructions and drug content on tension was observed, with tension increasing only in those knowingly receiving caffeine.
Conclusions:
- Participant knowledge of caffeine consumption significantly influences subjective and physiological responses.
- The findings question the generalizability of results from traditional double-blind studies to real-world scenarios.
- Future research should consider the role of expectation in caffeine's effects.