## 4 Discussion
### A Roadmap for Future Research in Aromachology  
What would, then, be the most important future avenues for future research? A good starting point is to look at the shortcomings of the available literature that may explain these inconsistent results. There appears to be at least three areas that should productively be explored in future research. Firstly, nearly all studies have dealt with the experimental data at the aggregated level, basically by simply comparing averaged data (e.g., dwell time, sales) against a control condition. This is notwithstanding the large and growing scientific evidence pointing at substantial individual differences in odor perception--due to genetics, demographics, habits, etc. [51; 52; 53; 54; 55; 56]. This variability pertains to all aspects of olfaction, such as the specific quality of the perception (how does a scent test to different consumers), its perceived intensity (how strong it will be experienced as), and its valence (is it going to be perceived as pleasant or unpleasant). For example, the aging process is known to affect odor sensitivity. Ability to perceive and identify smells peaks with early childhood and declines steadily afterwards so that, generally, older individuals can be expected to be less sensitive to odors than younger ones [55; 57]. This may be an issue of the prevalent practice of using students for selecting scenting and pre-testing their intensity, as students are generally young individuals whose olfactory functioning may not be representative of that of the end consumers (for instance, a scent may be experienced as strong by a 20-year-old person but may be very faint, or even undetectable, to a person aged 60). Likewise, men and women are known to differ in their sensitivity to smells [56; 58; 59; 60], and accordingly, several studies report significant findings only when analyzing the results for men and women separately [37; 44]. The differences are due to the individual genetic makeup, most of which are likely still unknown, that may cause individual differences in the possibility to perceive certain odors [54]. While the latter may not be relevant in the context of studies in actual retailing, phenotypical differences as a minimum have to be expected and accounted for. Finally, even if one could keep these perceptual differences invariant, there might still be differences in the importance different consumers ascribe to smells in the context of the shopping experience [61]. Therefore, the first recommendations for future research in aromachology are to move away from aggregate-level analyses in favor of analyses that account for individual differences, and secondly to ensure that the characteristics of the individuals involved in pre-testing and scent selecting match as much as possible those of the final consumers. Secondly, nearly all papers included for review focused on varying ambient scents while minimizing variation in other store atmospherics factors. This suggests that the external validity of current research in aromachology may be limited due to the multitude of other environmental factors (such as lightning, decor, musical background, etc.) and sensory inputs that may influence the customers' in-store experience [3; 4; 9; 14]. It is telling here that out of the only two studies that investigated additional factors, both reported significant interactions between in-store atmospherics. The study by [PERSON] and collaborators [42] found a significant two-way interaction between scent (presence vs. absence) and music (high vs. low volume) on arousal and ultimately time and money spent in the store. The study by [PERSON] and [PERSON] also manipulated scent and music and found that when scent and music are congruent with each other, customers rated the environment significantly more positively and bought more than when these store atmospherics factors were at odds with each other [40].