Logging of User Behavior

As a starting point for analysis, the total amount of time spent using the application and the total number of interactions carried out by the user has been counted for each participant. However these absolute measurements heavily depend on the performance of the Computer Vision API. Therefore the approach for analyzing the logged data was to calculate relative measures that are independent from external factors.

Differences in Browsing Rate

With regard to the observations made in the pilot study and during usability testing, the aim of the analysis of the logged data was to search for differences in the browsing behavior of the participants. To investigate this, the number of browsing interactions (i.e. the user tapping on a preview image) has been counted and divided by the total amount of user interactions for each of the participants. In this way, the browsing rate parameter that indicates the percentage of browsing during the interaction could be collected and compared between the participants.

of the participants had browsing rates of 8.9%, 8.3%, 7.0% and 0.7% respectively (average 6.2%) while the other three had browsing rates of 23.2%, 17.6% and 14.3% (average 18.4%). In other words, out of the 151 browsing interactions counted in total, 121 (80.1%) were executed by three of the seven participants and only 30 (19.9%) by the other four. The group of participants that preferred browsing are called browsing participants, with the other group being referred to as non-browsing participants.

Differences between Browsing and Non-Browsing Participants

In the same way the browsing rate has been calculated, the photograph rate has been gathered as additional parameter that indicates the percentage of photographing interactions.

While not being significantly different, the photograph rate is slightly lower for all browsing participants (29.9%, 26.2% and 26.2%: average 27.4%) compared to each of the non-browsing participants (35.3%, 32.6%, 31.7% and 31.3%: average 32.7%). One possible explanation for this difference is that a non-browsing participant takes a new photograph whenever the tags of the previous query are not sufficient, while a browsing participant starts to browse through images of the query and therefore does not need a new photograph.

Another comparable relative measure is the rate of user interactions per minute. This parameter is obtained by dividing the total number of interactions by the total time spent using the application. The average user interactions per minute for non-browsing participants (4.8 interactions per minute) is lower than for browsing participants (5.4 interactions per minute). This possibly results from the fact that browsing often incorporates rather quick jumping from one picture to the next, which incorporates comparatively many tapping interactions in a short period of time.

Although absolute measures should be interpreted very cautiously, it is worth noting that the average time spent using the application is higher for browsing participants (38 minutes and 36 seconds) compared to non-browsing participants (26 minutes and 18 seconds) and the average number of total interactions per user is also much higher for browsing participants (209) compared to non-browsing participants (124). This could be an indicator that browsing is more time consuming an involves more interactions compared to a non-browsing behavior.

Differences in Photograph Delete Rate

In the same way that the browsing rate and the photograph rate have been obtained, the delete rate can be retrieved and signifies the percentage of delete operations compared to the total number of operations executed by the user. Delete rates on

their own fluctuate for all participants between 16.8% and 31.3% with an average of 22.4%. There are no significant differences between browsing participants (average 21.8%) and non-browsing participants (average 22.9%).

However another interesting parameter can be retrieved from this data: When dividing the delete rate by the photograph rate, one can obtain the photograph delete rate. This parameter signifies the percentage of queries that the participant deleted. A photograph delete rate of 100% means the participant eventually deleted every query that he created, while a photograph delete rate of 0% means that the participant deleted none of the queries he created. In other words: Participants with lower photograph delete rates rather tend to keep queries instead of deleting them. Indeed there are significant differences between photograph delete rates: Three participants exhibit a photograph delete rate of 95.7%, 91.5% and 85.5% respectively (average 90.9%) while the other four only have 68.8%, 63.6%, 61.1% and 53.1% (average 61.7%). The latter group that tends to keep queries is referred to as the

keeping participants while the former are called non-keeping participants.

Differences between Keeping Participants and Non-Keeping Participants

When comparing participants’ types with regard to browsing and keeping queries, it is salient that all but one browsing participants are non-keeping participants and all but one non-browsing participants are keeping participants (see table 5.2). This observation could explain why the photograph rate is not significantly lower for browsing participants: Even though browsing participants should need fewer photographs in the first place, they also tended to delete their queries more often than non-browsing participants and therefore needed to take new photographs more often, which levels out the photograph rate compared to non-browsing participants.

Tab. 5.2: Different participants and groups assigned to them

Participant number: 1 2 3 4 5 6 7

Keeping participant (+) or not (-) - + - + - + + Browsing participant (+) or not (-) - - + - + + -

When investigating absolute measures of both groups, a big difference in the average time spent using the application can be seen: While keeping participants spent an average time of 25 minutes and 3 seconds with the application, non-keeping participants used it 40 minutes and 16 seconds. One explanation for this could be that keeping participants can use keywords from older queries while non-keeping participants need to retrieve them once again.