The Size of the Cookie Banner as a Choice Architecture Element

Looking at the data retrieved for the above experiment, we observed that in absolute terms, more people interacted with the treatment banner compared to the control though less people visited the website on the days with treatment banner. In other words, the interaction rate, defined as the percentage of visitors interacting with a cookie banner, was higher for the treatment banner than the control banner. This could not be explained by our original hypothesis. As the only change between the days with the control and treatment banner was the choice architecture of the banners, we hypothesise that:

H2: The interaction rate is dependent on the choice architecture of the cookie banner.

We conducted a Fisher’s exact test for comparing the interaction rate for both cookie banners in order to test the above stated hypothesis. We found that the interaction rate was significantly higher

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Control banner Treatment banner

Consent rate

Condition p value < .001

for the treatment cookie banner (37.8%) compared to the control banner (28.1%) (p < .001). The observed data is shown in Table 6 below.

Table 6

Observed website visitors compared to observed cookie banner interactions

Outcome measure Control banner Treatment banner n

Interaction 28.1% (219) 37.8% (270) 489

Non-interaction 71.9% (560) 62.2% (444) 1004

Number of visitors 779 714 1493

Note. The percentages of users interacting and not interacting with the cookie banners. The numbers in parentheses is the absolute number of users interacting and not interacting.

The result suggests that the choice architecture of cookie banners not only affects the actual decision of accepting or declining cookies, but also the decision about making a decision, that is whether to click the cookie banner or ignore it. This is important for our main analysis because a non-interaction results in no cookies being stored on the user’s device, as the GDPR requires consent prior to storage. Hence, a non-interaction is equal to rejecting cookies. The initial analyses showed that the majority of users who interacted with a cookie banner accepted cookies (71.7% for the control and 98.5% for the treatment banner). The lower interaction rate of the control banner, therefore, results in less visitors accepting cookies. In order to reveal a possible explanation for the difference in interaction rates, we revisited the cookie banners.

We identified three possible explanations for the difference in interaction rate, which were: 1) the control banner does not guide the user in his choice increasing cognitive load, causing him to refrain from making a decision, 2) the increased salience of the accept button on the treatment banner decreases the effort needed to make a decision, and 3) the treatment banner is larger than the control banner, thus, covers more of the screen. The larger size of the treatment banner increases salience of the banner and becomes bothersome to users who want to view the content hidden behind the cookie banner. Hence, causing more users to interact with the banner.

The two first possible explanations, lack of guidance on the control banner and increased salience of the accept button on the treatment banner, cannot be assessed individually as they are part of the

total choice architecture mechanism manipulated. The size of the cookie banner can, however, be assessed individually by exploiting that the cookie banners’ size differs between computers and mobile phones. This difference is due to the website being responsive, which means that content changes size according to the device in order to provide the best user experience. To investigate the size difference, we used a laptop with a screen size of 15.6 inches and a resolution of 1,366 x 768 pixels, and a smartphone with a screen size of 6 inches and a resolution of 2,160 x 1,080 pixels. The cookie banners on the two devices are shown below.

Figure 12: Control banner Figure 13: Control banner, laptop mobile

Figure 14: Treatment Figure 15: Treatment banner, laptop banner, mobile

We measured the size of the two cookie banners and compared them to the screen size of each device. On the laptop screen, the control banner covered 15.2% of the screen while the treatment cookie banner covered 19.3% of the screen, resulting in an average screen coverage of 17.3% On the smartphone screen in portrait (vertical) view, the control banner covered 24.3% of the screen compared to the treatment banner which covered 38.2% of the screen, resulting in an average screen coverage of 31.3%. The screen and cookie banner dimensions are shown in the Table 7 below.

Table 7

Cookie banner dimensions on the different devices

Device Control banner

dimensions

Treatment banner dimensions

Average cookie banner screen coverage 15.6 inch laptop screen

(19.4 cm x 34.5 cm) 3 cm x 34.1 cm

(15.2%) 3.8 cm x 34.1 cm

(19.3%) 17.3%

6 inch smartphone screen (13.6 cm x 6.8 cm)

3.3 cm x 6.8 cm (24.3%)

5.2 cm x 6.8 cm (38.2%)

31.3%

Note: The percentages indicate how many percent of the screen are occupied by the cookie banner

Both cookie banners occupied a larger percentage of the screen on the smartphone compared to the laptop. To test whether the size mattered for the interaction rate we posited the following

hypothesis:

H3: The interaction rate is dependent on the size of the cookie banner.

Following H3, we expected the interaction rate for mobile users to be higher compared to the interaction rate for laptop and desktop users. We separated the data for mobile and tablet users from laptop and desktop users, both for website visitors as well as for the interactions with the cookie banners (see Table 8).

Table 8

Interaction rates for mobile/tablet users and laptop/desktop users

Mobile/tablet Interaction Non-interaction Visitors

Control, mobile/tablet 40.4% (65) 59.6% (96) 161

Treatment, mobile/tablet 57.5% (111) 42.5% (82) 193

Total, mobile/tablet 49.7% (176) 50.3% (178) 354

Laptop/desktop

Control, laptop/desktop 24.9% (154) 75.1% (464) 618

Treatment, laptop/desktop 30.5% (159) 69.5% (362) 521

Total, laptop/desktop 27.5% (313) 72.5% (826) 1139

To test H3, we conducted a Fisher's exact test to compare the average interaction rate for mobile and tablet users to the average interaction rate for laptop and desktop users. As hypothesized, the interaction rate was significantly higher for mobile and tablet users (49.7%) compared to desktop and laptop users (27.5%) (p < .001).

Under the assumption that mobile and computer users are alike, the only variable that changes from mobile to desktop/laptop is the size of the cookie banner. The other choice architecture elements are constant regardless of device. As such, these results suggest that the size of the cookie banner has an effect on whether users interact with a cookie banner or not. The higher interaction rate of the

treatment banner compared to the control banner could therefore also in part be explained by the larger size of the treatment banner. Hence the size can be used as a tool within the choice

architecture to alter people’s behaviour.