Do double-blind studies with informed consent yield externally valid results?
- 139 Downloads
Subjective and physiological effects of caffeine were investigated via a 3×2×3 design that assessed independent and interactive effects of instructions (told caffeine versus told no caffeine versus not told whether beverage contained caffeine), actual beverage content (caffeine versus no caffeine), and time after ingestion (15, 30, and 45 min). Instructions affected altertness at 15 min after ingestion. Caffeine increased alertness at 30 min after ingestion and systolic blood pressure at 30 min and 45 min after ingestion. A highly significant instruction by drug interaction on tension was obtained at all measurement points, indicating an increase in tension only among subjects who knowingly received caffeine. Because people are generally informed of drug content in non-research settings, these data challenge the external validity of typical double-blind studies, in which subjects are informed of the possibility of receiving a placebo as part of the consent procedure.
Key wordsCaffeine Placebo Expectancy Double-blind design Informed consent
Unable to display preview. Download preview PDF.
- Faden RR, Beauchamp TL (1986) A history and theory of informed consent. Oxford University Press, New YorkGoogle Scholar
- Fillmore M, Vogel-Sprott M (1992) Expected effect of caffeine on motor performance predicts the type of response to placebo. Psychopharmacology 106:209–214Google Scholar
- Hughes JR, Gulliver SB, Amori G, Mireault GC, Fenwick JF (1989) Effect of instructions and nicotine on smoking cessation, withdrawal symptoms and self-administration of nicotine gum. Psychopharmacology 99:486–491Google Scholar
- Kirsch I, Weixel LJ (1988) Double-blind versus deceptive administration of a placebo. Behav Neurosci 102:319–323Google Scholar
- Lane JD (1983) Caffeine and cardiovascular responses to stress. Psychosom Med, 45:447–451Google Scholar
- Lane JD, Williams RB (1987) Cardiovascular effects of caffeine and stress in regular coffee drinkers. Psychophysiology 24:157–164Google Scholar
- Marlatt GA, Rohsenow DJ (1980) Cognitive processes in alcohol use: Expectancy and the balanced placebo design. In: Mello NK (ed) Advances in substance abuse: behavioral and biological research, JAI Press, Greenwich, CT, pp 159–199Google Scholar
- Penick SB, Fisher S (1965) Drug-set interaction: Psychological and physiological effects of epinephrine under differential expectations. Psychosom Med 27:177–182Google Scholar
- Penick SB, Hinkle LE (1964) The effect of expectation on response to phenmatrizine. Psychosom Med 26:369–373Google Scholar
- Reinsenzein R (1983). The Schachter theory of emotion: two decades later. Psychol Bull 94:239–264Google Scholar
- Rickels K (1986) Use of placebo in clinical trials. Psychopharmacol Bull 22:19–24Google Scholar
- Robertson D, Frölich JC, Carr RK, Watson JT, Hollifield JW, Shand DG, Oates JA (1978) Effects of caffeine on plasma renin activity, catecholamines and blood pressure. N Engl J Med 298:181–186Google Scholar
- Schachter S, Singer J (1962) Cognitive, social and physiological determinants of emotional state. Psychol Rev 69:379–399Google Scholar
- Wigmore ST, Hinson RE (1991) The influence of setting on consumption in the balanced placebo design. Br J Addict 86:205–215Google Scholar