quantified by fitting consumption curves for constant-priced alternative commodities using the exponential equation (Hursh and Roma, 2013, 2015):
in which the free parameter Qalone is asymptotic consumption of a constant- priced, alternative commodity when the price (P) of a price-manipulated commodity is infinitely high; I is the y-axis span of consumption in log10 units, describing the degree of interaction between commodities; and b is sensitivity of alternative product consumption to reductions in consumption of the price-manipulated commodity. Here, negative values of the I term indicate substitution between commodities and positive values indicate complementarity.
In the following sections, we review historical and contemporary methods used to assess the behavioral economics demand measures outlined above.
We organize these sections according to the four epochs of methods innovation, highlighting important findings from each epoch that have contributed to our understanding of tobacco regulatory science.
Behavioral economics 1.0: operant self-
magnitude of the reinforcer (i.e., minimizing puff volume) while keeping the fixed ratio requirement (i.e., plunger pulls) constant. When these two methods of manipulating unit price were directly compared, cigarette puff consumption was consistent, regardless of whether the ratio requirement was increased or puff magnitude was decreased (Bickel et al., 1991).
Interestingly, participants also consumed consistent numbers of puffs at each unit price, regardless of incremental progressive ratio increases or random ratio dictated unit price (Giordano et al., 2001). Interventions attempting to manipulate puff consumption were largely unsuccessful at the time, indicating that puff consumption is consistently sensitive to unit price.
However, puff intake was manipulated under specific conditions. For example, cigarette puff intake was more elastic (i.e., decreased more readily with increasing unit prices) when smokers were acutely deprived (Madden and Bickel, 1999). Although these effects were small and waned over time, they supported the notion that consumption may be manipulated temporarily depending upon the circumstances of the consumers’ environment. Finally, while different commodities such as conventional cigarettes and de- nicotinized cigarettes are sensitive to increasing prices, interactions between commodities can occur when alternative rewards, such as money, are available concurrently (Shahan et al., 2001).
Preference for alternatives
In a review and re-analysis of 16 studies, findings from the drug self- administration laboratory using different species, drug classes, and procedures demonstrated that concurrently available commodities could act as substitutes, independents, or complements (Bickel et al., 1995). The interaction type between commodities occurs depending on the concurrently available alternatives, their magnitude, and the relative price of each (Bickel et al., 1995). For example, when conventional and de-nicotinized cigarettes were available alone with increasing prices, each produced similar elasticities of demand, consistent with price sensitivity. However, when participants were given the choice between the two concurrently available commodities at equivalent prices (i.e., fixed ratio requirements), participants chose conventional cigarettes significantly more over de-nicotinized cigarettes (Shahan et al., 1999), indicative of greater valuation of conventional
cigarettes. Interestingly, in other cases the presence of some commodities may have no effect on consumption at all, in which case the commodities are considered independents. For example, when cigarette puffs and money were available concurrently, the increase in unit price of cigarette puffs did little to affect preferences for the money condition (DeGrandpre et al., 1994). Similar operant procedures demonstrated that when unit price for cigarette puffs (i.e., fixed ratio) was increased, coffee consumption decreased alongside cigarette consumption, indicative of complementary commodities (Bickel et al., 1992).
Increasingly complex combination studies were introduced to the laboratory to answer questions such as, “Do smokers differentially consume tobacco products when alternatives are available?” For example, cigarettes, nicotine gum, and/or money were presented alone first and then in combination (Johnson and Bickel, 2003). As illustrated in Figure 3.1, cigarette puff consumption decreased with increasing unit price in all conditions, as expected. Interestingly, when cigarettes and gum were presented concurrently, gum substituted for cigarettes as the price of cigarettes increased, whereas money was again independent of the cigarette price increase. When all three commodities were available together, the total consumption of cigarette puffs decreased, supporting the notion that the presence of substitute and independent reinforcers can reduce cigarette intake (Johnson and Bickel, 2003). An expansion of these methods found that with increasing prices of conventional cigarettes, both de-nicotinized cigarettes and nicotine gum functioned as substitutes (i.e., when only two commodities were available). However when all three commodities were available together, de-nicotinized cigarettes were more reliably chosen over the gum as an alternative (Johnson, Bickel, and Kirshenbaum, 2004). Again, these combination studies highlight how consumers will alter their purchasing when presented with alternatives and can help researchers predict consumer behavior in more realistic environments.
FIGURE 3.1 Group mean (±SEM; n=11) self-administrations of cigarette puffs, nicotine gum, and/or money presented as a function of increasing unit price for cigarettes. Each of four phases
demonstrates differential self-administration dependent on the commodities available. Consistent with early work using linear demand analysis with the log of both axes, zero values were replaced with trivially small nonzero values (in this case, 0.5).
Although operant procedures such as those described above allow researchers to generate demand curves and directly measure the interactions between concurrently available commodities and their self-administration in the laboratory, weaknesses exist for this approach. First, multi-session
laboratory-based progressive ratio procedures are highly staff- and time- intensive, each session lasting several hours, and requiring expensive specialized equipment. Second, in single session studies, breakpoints, where individuals stop responding for the reinforcer, can be obtained, however demand curves cannot be generated and participants may become fatigued and/or satiated (Hursh and Silberberg, 2008). Practical barriers, such as the cost of building or renovating laboratory space with air filtration systems to safely conduct these laboratory smoking studies, can be costly and are necessary to reduce the risk of participants and study staff breathing second- hand smoke. While some of these limitations remain in the preclinical non- human laboratories, more recent clinical work has obtained reliable and consistent data using participant self-report measures.