An important and controversial issue in system design involves screen density and window size in both single and multiple window displays. How much information should we put into a window? If several windows can be viewed at the same time, should we display many small windows or only a few larger windows? What affect do these decisions have on performance? Because of the current popularity of the web and the functionality of hypertext interfaces in general, we chose to study the effect of window size on web browser performance in order to answer some of these questions.
The main factors that previous research brings to light is that scrolling tends to be increased when the size of a window is decreased which, in turn, has a deteriorating effect on performance. Subjects tend to be more satisfied with larger viewing areas and efforts to eliminate the need for scrolling a window seem to be worthwhile. Higher density screens will improve search times for experienced users, but lower densities have higher subjective satisfaction ratings.
Staggers (1993) performed an experiment on nurses using Hospital Information System (HIS) screens of varying densities. Density was defined to be the number of characters divided by the total number of spaces on each screen. One system contained three low density screens, another contained two moderate density screens and the third contained one high density screen. One important finding of this study was that with practice, all nurses saw a dramatic performance improvement on all three systems. The most significant finding of this study was that the search time to find targets was significantly lower on the system with one high density screen and that the accuracy in finding targets was similar in all three systems. This shows that the interfaces of current Hospital Information Systems can be improved by increasing the density of output screens without sacrificing any accuracy in obtaining results.
Plaisant, et al. (1996) was working on a web interface for the Library of Congress National Digital Library Program and discovered that the HTML tables feature, which was new at the time, enabled them to increase the density of their main screens, which significantly reduced scrolling. The tables placed boundaries around the hypertext links and gave them logical separation, allowing them to be physically closer without confusing users of the system. This condensing technique has become quite popular on the web and improves search time for finding links by limiting or eliminating the need for scrolling.
One study compared the effectiveness of different window sizes in program reading (Reisel and Shneiderman, 1986). Window sizes of 10, 22, 60, and 120 lines were used by undergraduate computer science majors to answer questions about different programs. Typical questions required the students to count a number of specific features in the program as well as locate specific expressions. The results showed both increasing accuracy in answering questions and decreasing numbers of page turns as the window size increased. Subjective reactions showed that the students were most frustrated with the 10-line display, as predicted, because of the constant need to scan through the program in small steps to locate specific areas. In contrast, experimenters observed that students using the 120-line display were able to look from location to location rather than scanning, which indicates that they were able to remember the location of specific parts of the program.
A review of Sony's WebTV system (Nielsen, 1997) shows the importance of viewing area size. This product enables people who do not own computers to view the World Wide Web on their TV screens. The author of this review found that one of WebTV's most serious problems was the lack of content displayed per screen when compared with a traditional computer monitor. This is partly due to the poor resolution of NTSC television signals as well as the need to make text large so that it can be read from the user's couch. This constraint on viewing area creates the need for extreme amounts of scrolling to view the entire page. It also makes it difficult to determine the structure of the page and therefore predict what kinds of things could be found with additional scrolling.
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