Introduction

The Princeton Review offers these three levels of online individualized SAT tutoring on its website:

• SAT Private Level 24-hr Online Tutoring Package
• SAT Master Level 24-hr Online Tutoring Package
• SAT Premier Level 24-hr Online Tutoring Package

In order to purchase a package, a customer must first enter in a ZIP code. Students at Harvard University found that entering different ZIP codes resulted in different prices [1]. We improved on their original scraper, and in July and August 2015, we downloaded a list of prices for each package by ZIP code. We found that for each package those prices varied.

We sought to understand whether The Princeton Review’s pricing system might disproportionately assign higher prices based on demographic characteristics, a phenomenon that has been found in other online pricing by ZIP code.

Background

All three of The Princeton Review’s online SAT tutoring packages varied in price by geography. Depending on ZIP code, users saw one of three potential prices for the Private and Master packages. The most expensive package, Premier, displayed one of four possible prices by ZIP code.

The remainder of this paper will focus on the Premier package. For that package, prices ranged from $6,600 to $8,400, as shown in Table 1.

Table 1. Number of ZIP codes in the United States for each of the prices quoted for The Princeton Review’s SAT Premier Level 24-hour Online Tutoring Package.

The Princeton Review's Premier prices are regionally distributed, with higher prices in California, the North East, most of Illinois and Wisconsin, Houston, Texas, and Cheyenne, Wyoming. (Figure 1).

Figure 1. The areas with the lowest price are shaded in tan ($6,600). The orange areas are the second highest price ($7,200). The dark orange areas are the third-highest price ($7,800). Red represents the highest price, which is not discernable at this scale, and includes most of New York City region.

Methods

We used census data to get a better understanding of the people who lived in these ZIP codes. We used the U.S. Census' ZIP Code Tabulation Areas (ZCTAs) [2], which are slightly different than the ZIP codes managed by the Postal Service. (For more see the Census' explanation of how ZCTAs are created. [3]) For this analysis, ZCTAs were the only viable geographic unit.

We used the following selected demographic fields from the 2013 5-year American Community Survey data [4] for our analysis.

1. Race, from Census Table B02001
2. Median Household Income in the Past 12 Months, from Census Table B19013
3. Educational Attainment, from Census Table S1501

The total number of ZCTAs used in this study was 26,892 of the 33,144 total ZCTAs. We ignored 6,252 ZCTAs because of large sampling errors or missing data.

The ZCTA demographic data allowed us to assess the relationships between characteristics of ZCTAs residents and The Princeton Review’s price.

A logistic regression suggested candidate demographic variables for further analysis. We found that when controlling for factors like race and educational attainment, higher income ZCTAs had higher odds of being quoted a higher price by The Princeton Review. We also found that ZCTAs with higher percentages of Asian residents were more likely to be quoted one of the higher prices (For regression model results, see Figure 2).

We then conducted risk ratio analyses for Asians versus non-Asians and people in living above median-income ZCTAs versus below median-income ZCTAs.

Results

For regression model results, see Figure 2.

Figure 2. A Logistic Regression Model for The Princeton Review's Pricing Scheme.

The combined ZCTA demographic and pricing data allowed us to generate a contingency table, as seen in Table 2.

A comparison of the rates at which Asians and non-Asians live in The Princeton Review’s higher pricing ZIP codes resulted in an incidence rate ratio of 1.8, meaning that Asians are nearly twice as likely as non-Asians to be offered one of the higher price levels by The Princeton Review.

Table 2. Asian vs. Prices Contingency Table.

Similarly, we generated a contingency table comparing ZCTAs with median household income above $73,632 to ZCTAs with median household income below that threshold. We chose $73,632 because it is one standard deviation away from the mean of the median incomes for ZCTAs.Table 3.

The incidence rate ratio was 2.05, which means that Americans living in areas with higher household income were twice as likely as those in low-income areas to be charged a higher price by The Princeton Review.

Table 3. Income vs. Prices. Contingency Table.

It could be argued that Asians are offered high prices for these courses because they live in wealthier areas. To test this proposition, we divided the ZCTAs in our analysis into categories: those with median household incomes above the U.S. national median income, and those below.

Our analysis showed, however, that even after isolating low median income ZCTAs, Asians had a disproportionate likelihood of being offered a high price by The Princeton Review, generating an incidence rate ratio of 2.2 as seen in Table 4. Isolating higher-income ZCTAs, somewhat narrows the incidence rate ratio to 1.4, as seen in Table 5.

Since the New York City metropolitan area is an outlier in the data, in that the entire area is assigned the higher price, we conducted a sensitivity analysis to see if removing the city’s ZCTAs significantly changed our findings. The results remained consistent.

Table 4: Contingency Table for Asians in areas with median incomes below the national median income of $53,046.

Table 5: Contingency Table for Asians in areas with median incomes above the national median income of $53,046.

Discussion

Our analysis found that Asians were almost twice as likely as non-Asians to live in one of the areas being offered the higher price levels by The Princeton Review. And this effect remained consistent when stratifying ZCTAs by median income. We also found that residents of relatively high income ZCTAs were much more likely to be offered one of The Princeton Review’s higher price levels. A more comprehensive examination of the issues raised by this analysis can be found in a news article on ProPublica’s website. [5]