Understanding Web User Behaviour

A series of observational studies of Web user behaviour were undertaken in order to learn more about how users made link activation decisions. Fourteen subjects were recruited with varying degrees of Web experience and expertise in computer use, ranging from novices to experts. Data about subject browsing behaviour was automatically logged by using a proxy server connected to the Web client. This parsed the HTML pages that the subject downloaded and recorded the URL, number of images, number of links, number of applets and the download time from the proxy request to the proxy receiving the data. Each browsing session was also recorded using video and audio.

At the end of the session, all the collected data -- video, audio and proxy logs -- was reviewed and a detailed transcript of the session was produced. A re-enactment protocol was then employed to elicit from subjects the reasoning behind their actions [28]. All the utterances of the subject and the investigator were recorded on audio cassette and later transcribed.

Analysis of this data leads us to propose a three phase model of user link activation decision-making behaviour:

Assessment of value

The user must decide prior to activating a link whether the referenced document contains information that is useful with respect to the user's overall objective. Reaching a positive assessment will lead to the link being activated and the download of the referenced document will commence; a negative assessment will result in the link being ignored. In addition to the assessment of the referenced document's content, the user also makes an assessment of the likely download quality of service (QoS). The potential of a long wait (e.g., because of server or network congestion, low network bandwidth) for the referenced document may persuade a user to ignore the link, or at least ignore the link for the present until a more favourable time. Our subjects often tried to infer by the URL information about the probable length of the wait. Here, heuristics and rules of thumb prompted by previous experience often come into play. For example:

``This page is on a University server and that means it should be quick because they have fastish servers.'' (Subject C)

The assessment of value process that the user undertakes prior to activating a link can therefore, be split into two parts:

1.

an assessment of content, and

2.

an assessment of download QoS, particularly the anticipated delay in downloading the document.

Download

Once the link has been activated, the document download begins. During this phase the user is exposed to the underlying behaviour of the communication network. As we noted above, users of interactive systems are often very sensitive to delays, especially where these are of an unpredictable extent. The problem takes on even greater significance for the Web, however, because browser user interfaces allow users to interrupt and abandon the download at any time. In our studies, observations of users choosing this option were very common.

Johnson has employed micro-economic cost-utility models and the notion of marginal utility to analyse Web user responses to download delays [15]. He demonstrated that users' tolerance of delays could be manipulated by increasing their expectations of document quality. Johnson's findings are evidence for the close relationship between the assessment of value phase and the download phase; by increasing the information available to the user before they activate the link, the user is not only better informed about its nominal value, but is also better able to make an informed decision about whether the document is worth waiting for.

Some of our subjects revealed interesting beliefs about the extent to which their actions could influence the download time. For example, several subjects articulated the view that slow downloads could be speeded up by stopping and restarting them. When asked to explain this, one user drew upon a telephone analogy:

``...[it] is like a crackerly telephone line, if you ring again the quality is often better.'' (Subject E)

Others provided more technically sophisticated rationales for their behaviour:

``...when you stop and reload, it is possible to get a better route for the data, so it may be quicker.'' (Subject G)

``...there is only a certain number of connections that a server can make, by reloading a page a new connection may have become free due to a time out or other users disconnecting.'' (Subject D)

Evaluation

The final phase allows a user to evaluate the outcome of activating the link. If the activation was successful, the referenced document can be perused and its content can be compared with the expectations generated by the assessment of value phase. Similarly, the download performance can be evaluated. The evaluation process may stimulate the formation of heuristics that will serve to make sense of the experience, and which may then come into play in future cycles of interaction. A flavour of these heuristics is evident in explanations given by our subjects such as:

``...all sites in Australia are slow.'' (Subject A)

``...it is night time in America so all information will be transferred very fast.'' (Subject I)

  

Figure 3: The constituent parts of a URL.

It was evident from subjects' comments that the URL was often an important element in the assess-download-evaluate cycle. The URL could be used to predict the content of the referenced document, the location of the Web site and the download time in the Assessment of value phase. In the Evaluation phase, in retrospectively comparing the outcome with their initial expectations, users would try to (re)-interpret the URL in a way that was consistent with the outcome, the spatial location of the site and the time taken for data transfer.

These observations led to the design of a second study to investigate what information users can extract from the URL and how this may figure in the link activation decision. Eighteen subjects with varying degrees of Web experience and expertise in computer use were recruited. Each one was shown a list of URLs and asked to predict what he or she thought the referenced document was, and to predict its download behaviour. Subjects were then shown the actual referenced document and asked to assess the accuracy of their prediction.

The results indicated that more experienced subjects were able to deconstruct a URL into its constituent parts (see Figure 3). Generally, a ``full'' prediction would include inferences about geographical location from the hostname, about content from the pathname and filename, and about download behaviour from the file_type and hostname parts (i.e., from document type and location). In contrast, less experienced subjects were generally unable to distinguish between the constituent parts of the URL. Inferences about location, content and download behaviour were therefore based upon a decontextualised recognition of strings within any part of the URL.

In Figure 4 we show extracts from transcripts of session protocols. Interviewer's and subject's comments are distinguished by (I:) and (S:) respectively. The first extract shows the kind of inferences made by a typical novice subject. The next three extracts illustrate the kinds of inferences made by more experienced subjects.

  

Figure 4: Extracts from transcripts of session protocols from the second study.

Informed by the results of these investigations, we now turn to consider in more detail how the usability objectives defined earlier may be tackled. Our discussion will focus on two broad areas in turn: documents and links.