Kaushik Basu used
game theory in 1997 to argue that rational consumers value their own time and effort in calculation. Such consumers process the price from left to right and tend to mentally replace the last two digits of the price with an estimate of the mean "cent component" of all goods in the marketplace. In a sufficiently large marketplace, this implies that any individual seller can charge the largest possible "cent component" (99¢) without significantly affecting the average of cent components and without changing customer behavior. Ruffle and Shtudiner's (2006) laboratory test shows considerable support for Basu's 99-cent pricing equilibrium, particularly when other sellers' prices are observable. The introduction of the
euro in 2002, with its various exchange rates, distorted existing nominal price patterns while at the same time retaining real prices. A European wide study (el Sehity, Hoelzl and Kirchler, 2005) investigated consumer price digits before and after the euro introduction for price adjustments. The research showed a clear trend towards psychological pricing after the transition. Further,
Benford's law as a benchmark for the investigation of price digits was successfully introduced into the context of pricing. The importance of this benchmark for detecting irregularities in prices was demonstrated and with it a clear trend towards psychological pricing after the nominal shock of the euro introduction. Another phenomenon noted by economists is that a
price point for a product (such as $4.99) remains stable for a long period of time, with companies
slowly reducing the quantity of product in the package until consumers begin to notice. At this time, the price will increase marginally (to $5.05) and then within an exceptionally short time will increase to the next price point ($5.99, for example). Several studies have shown that when prices are presented to a prospect in descending order (versus ascending order), positive effects for the seller result, mainly a willingness to pay a higher price, higher perceptions of value, and higher probability of purchase. The reason for this is that when presented in the former, the higher price serves as a reference point, and the lower prices are perceived favorably as a result.
In consumer behavior Thomas and Morwitz (2005) suggested that this bias is a manifestation of the pervasive anchoring heuristic in multi-digit comparisons. (The anchoring heuristic is one of the heuristics identified by Nobel laureate Kahneman and his co-author Tversky.) Judgments of numerical differences are anchored on leftmost digits, causing a bias in relative magnitude judgments. This hypothesis suggests that people perceive the difference between 1.99 and 3.00 to be closer to 2 than to 1 because their judgments are anchored on the leftmost digit. Stiving and Winer (1997) examined the left-digit effect using scanner panel models. They proposed that 9-ending prices can influence consumer behavior through two distinct processes: image effects and level effects. Image effect suggests that 99-ending prices are associated with images of sales promotions. Level effect captures the magnitude underestimation caused by anchoring on the leftmost digits of prices. Their results suggest that both of these effects account for the influence of 9-ending prices in grocery stores. Manning and Sprott (2009) demonstrated that left-digit anchoring can influence
consumer choices using experimental studies.
In consumer finance Psychological pricing has also been observed in consumer finance, particularly in the presentation of interest rates.
Patrick M. Brenner of the
Southwest Public Policy Institute has argued that the annual percentage rate (APR), introduced under the Truth in Lending Act, can function similarly to charm pricing by shaping borrower perception of cost. While APR was designed to standardize and simplify loan comparisons, Brenner contends that it may compress complex, long-term borrowing costs into a single figure that obscures total repayment. In this interpretation, small changes in the leftmost digit, such as mortgage rates falling from 6.00 percent to 5.98 percent, can influence consumer sentiment despite minimal underlying differences, reflecting the same left-digit bias observed in retail pricing. This framing encourages borrowers to focus on nominal rates or monthly payments rather than lifetime cost.
In financial markets Left-digit effect has also been shown to influence stock-market transactions. Bhattacharya, Holden, and Jacobsen (2011) examined the left-digit effect in stock market transactions. They found that there was excess buying at just-below prices ($1.99) versus round numbers ($2.00) right above them. This discrepancy in buy-sell can lead to significant changes in 24-hour returns that can meaningfully impact markets.
In public policy Research has also found psychological pricing relevant to the study of politics and public policy. For instance, a study of Danish municipal income taxes found evidence of "odd taxation" as tax rates with a nine-ending were found to be over-represented compared to other ending digits. Further, it was found that citizens' evaluations of public-school districts in a Danish population changed noticeably based on the leftmost digit. In particular, the researchers looked at minuscule changes in average grades that shifted the leftmost digit. Once this value changed, citizens responded more drastically and as such their stance in terms of public policy on the issue changed. MacKillop
et al. (2014) looked at how the left-digit effect affects the relationship between price hikes and
smoking cessation. There was a very clearly demonstrated inverse relationship between the price of cigarettes and individual's motivation to smoke. Researchers found that price hikes that impacted the leftmost digit in the price (i.e. $4.99 vs. $5.00) were particularly effective in causing change among adult smokers. These findings can be utilized by public policy researchers and legislators to implement more effective cigarette tax policies. == Regulation ==