A Comparison of Linear and Hypertext Formats in Information Retrieval
Cliff McKnight, Andrew Dillon and John Richardson
This item is not the definitive copy. Please use the following citation when referencing this material: McKnight, C., Dillon, A., and Richardson, J. (1990) A comparison of linear and hypertext formats in information retrieval. In R. McAleese and C. Green, Hypertext: state of the art, Oxford: Intellect, 10-19.
An exploratory study is described in which the same text was presented to subjects in one of four formats, of which two were hypertext (TIES and Hypercard) and two were linear (Word Processor and paper). Subjects were required to use the text to answer 12 questions. Measurement was made of their time and accuracy and their movement through the document was recorded, in addition to a variety of subjective data being collected. Although there was no significant difference between conditions for task completion time, subjects performed more accurately with linear formats. The implications of these findings and the other data collected are discussed.
It has been suggested that the introduction of hypertexts could lead to improved access and (human) processing of information across a broad range of situations (Kreitzberg and Shneiderman, 1988). However, the term 'hypertext' has been used as though it was a unitary concept when, in fact, major differences exist between the various implementations which are currently available and some (Apple's Hypercard for example) are powerful enough to allow the construction of a range of different applications. In addition these views tend to disregard the fact that written texts have evolved over several hundred years to support a range of task requirements in a variety of formats. This technical evolution has been accompanied by a comparable evolution in the skills that readers have in terms of rapidly scanning, searching and manipulating paper texts (McKnight et al., 1990).
The recent introduction of cheap, commercial hypertext systems has been made possible by the widespread availability of powerful microcomputers. However, the recency of this development means that there is little evidence about the effectiveness of hypertexts and few guidelines for successful implementations.
Although a small number of studies have been carried out, their findings have typically been contradictory (cf. Weldon et al.,1985, and Gordon et al., 1988). This outcome is predictable if allowances are not made for the range of text types (e.g., on-line help, technical documentation, tutorial packages) and reading purposes (e.g., familiarisation, searching for specific items, reading for understanding). Some text types would appear to receive no advantage from electronic implementation let alone hypertext treatment at the intra-document level (poetry or fiction, for example, where the task is straightforward reading rather than study or analysis of the text per se). Thus there appears to be justification for suggesting that some hypertext packages may be appropriate for some document types and not others. A discussion of text types can be found in Dillon and McKnight (1989).
Marchionini and Shneiderman (1988) differentiate between the procedural and often iterative types of information retrieval undertaken by experts on behalf of end users and the more informal methods employed by end users themselves. They suggest that hypertext systems may be well suited to end users because they encourage "informal, personalized, content-oriented information seeking strategies" (p.71).
The current exploratory study was designed to evaluate a number of document formats using a task that would tend to elicit 'content-oriented information seeking strategies'. The study was also undertaken to evaluate a methodology and indicate specific questions to be investigated in future experiments.
16 subjects participated in the study, 9 male and 7 female, age range 21 - 36. All were members of HUSAT staff and all had experience of using a variety of computer systems and applications.
The text used was "Introduction to Wines" by Elizabeth A. Buie and W. Edgar Hassell, a basic guide to the history, production and appreciation of wine. This hypertext was widely distributed by Ben Shneiderman as a demonstration of the TIES (The Interactive Encyclopedia System) package prior to its marketing as HyperTIES.
This text was adapted for use in other formats by the present authors. In the TIES version, each topic is held as a separate file, resulting in 40 individual small files. For the Hypercard version, a topic card was created for each corresponding TIES file. For the word processor version, the text was arranged in an order which seemed sensible to the authors starting with the TIES 'Introduction' text and grouping the various topics under more general headings. A pilot test confirmed that the final version was generally consistent in structure with the present sample's likely ordering.
The Hypercard and word processor versions were displayed on a monochrome Macintosh II screen and the TIES version was displayed on an IBM PC colour screen. The paper version was a print-out of the word processor text.
Subjects were required to use the text to answer a set of 12 questions. These were specially developed by the authors to ensure that a range of information retrieval strategies were employed to answer them and that the questions did not unduly favour any one medium (e.g., one with a search facility).
A four-condition, independent subjects design was employed with presentation format (Hypercard, TIES, Paper and Word Processor) as the independent variable. The dependent variables were speed, accuracy, access strategy and subjects' estimate of document size.
Subjects were tested individually. One experimenter described the nature of the investigation and introduced the subject to the text and system. Any questions the subject had were answered before a three minute familiarisation period commenced, during which the subject was encouraged to browse through the text. After three minutes the subjects were asked several questions pertaining to estimated document size and range of contents viewed. They were then given the question set and asked to attempt all questions in the presented order. Subjects were encouraged to verbalise their thoughts and a small tie-pin microphone was used to record their comments. Movement through the text was captured by video camera.
Estimates of document size
After familiarisation with the text, subjects were asked to estimate the size of the document in pages or screens. The linear formats contained 13 pages, the Hypercard version contained 53 cards, and the TIES version contained 78 screens. Therefore raw scores were converted to percentages. The responses are presented in Table 1 (where a correct response is 100).
Table 1: Subjects' estimates of document size.
Subjects in the linear format conditions estimated the size of the document reasonably accurately. However, subjects who read the hypertexts were less accurate, several of them over-estimating the size by a very high margin. While a one-way ANOVA revealed no significant effect (F[3,12] = 0.61, NS) these data are interesting and suggest that subjective assessment of text size as a function of format is an issue worthy of further investigation. Such an assessment may well influence an estimation of the level of detail involved in the content as well as choice of appropriate access strategy.
Time taken to complete the twelve tasks was recorded for each subject. Total time per subject and mean time per condition are presented in Table 2 (all data are in seconds).
Clearly, while there is variation at the subject level there is little apparent difference between conditions. A one-way ANOVA confirmed this (F[3,12] = 0.47, p > 0.7) and even a t-test between the fastest and slowest conditions, Hypercard and TIES, failed to show a significant effect for speed (t = 1.31, d.f. = 6, p > 0.2).
The term 'accuracy' in this instance refers to how many items a subject answers correctly. This was assessed by the experimenters who awarded one point for an unambiguously correct answer, a half-point for a partly correct answer and no points for a wrong answer or abandoned question. The accuracy scores per subject and mean accuracy scores per condition are shown in Table 3.
As can be seen from these data, subjects performed better in both linear-format conditions than in the hypertext conditions. A one-way ANOVA revealed a significant effect for format (F[3,12] = 8.24, p < 0.005) and a series of post-hoc tests revealed significant difference between paper and TIES (t = 4.13, d.f. = 6, p < 0.01), Word Processor and TIES (t = 3.13, d.f. = 6, p < 0.05) and between Paper and Hypercard (t = 4.11, d.f. = 6, p < 0.01). Even using a more rigorous basis for rejection than the 5 per cent level, i.e., the 10/k(k-1) level, where k is the number of groups, suggested by Ferguson (1959), which results in a critical rejection level of p < 0.0083 in this instance, the Paper/TIES and Paper/Hypercard differences are still significant.
The number of questions abandoned by subjects was also identified. Although there was no significant difference between conditions (F[3,12] = 1.85, NS) subjects using the linear formats abandoned less than those using the hypertext formats (total abandon rates: Paper = 1; Word Processor = 2; Hypercard = 4 and TIES = 9).
Time spent viewing the Contents/Index (where applicable) was determined for each subject and converted to a percentage of total time. These scores are presented in Table 4.
Table 4: Time spent viewing Contents/Index as a percentage of total time.
This table demonstrates a very large difference between both hypertext formats and the linear formats. A one-way ANOVA revealed a significant effect for condition (F[3,12] = 9.95, p < 0.005). Once more, applying the more conservative critical rejection level, post-hoc tests revealed significant differences between Paper and TIES (t = 4.90, d.f. = 6, p < 0.003), between Word Processor and TIES (t = 4.16, d.f. = 6, p < 0.006) and between Hypercard and paper (t = 3.06, d.f. = 6, p < 0.03). Thus, interacting with a hypertext document may necessitate heavy usage of indices in order to navigate effectively through the information space.
In general, subjects performed better with the linear format texts than with the hypertexts. The linear formats led to significantly more accurate performance and to significantly less time spent in the index and contents. Not surprisingly, estimating document size seems easier with linear formats.
While there was no significant effect for the estimation of document size data, a number of observations can be made. The accurate estimates for the Paper and Word Processor condition may well have resulted from the fact that the Contents pages indicated the total number of pages and that the page number was displayed for each page, and hence browsing through the document would have given repeated cues to the document size. Finally, in the Paper condition the subjects would have received tactile feedback as they manipulated the document.
Subjects in the hypertext conditions had none of this information to help them form an impression of the document's size. While many of the cards were discrete (i.e., there were few continuation cards) and were individually listed in the indices this information did not prevent some subjects from making large over-estimates. A poor estimate of document size could lead to incorrect assumptions concerning the range of coverage and level of a document and the adoption of an inappropriate reading strategy. Future studies might usefully explore the relationship between manipulation strategy and subjective impression of size for larger documents.
A number of factors are likely to have influenced the subjects' task completion times and as a result the lack of an overall speed effect is to be expected. These factors include variation in the subjects' familiarity with the topic area (wines); variation in the subjects' reading speeds; the presence or absence of a string search facility in the electronic versions; variation in the subjects' familiarity with the different software packages; and their determination to continue searching until an answer is found. However, there does not appear to be a speed/accuracy trade-off.
The strong effect found for the navigation measure appears to be consistent with the significant difference in accuracy scores between the four conditions. Subjects in the hypertext conditions spent considerably more time viewing the index and contents lists than did subjects in the linear conditions but were less successful in finding the correct answers to the questions. The hypertext systems elicited a style of text manipulation which consisted of selecting likely topics from the index, jumping to them and then returning to the index if the answer was not found. Relatively little time was spent browsing between linked nodes in the database. This is a surprising finding since hypertext systems in general are assumed to be designed with this style of manipulation in mind. It may be argued that a comprehension or summarisation task would have resulted in this style of manipulation but, in contrast to the above, subjects in the linear conditions tended to refer once to the Contents/Index and then scan the text for the answer rather than make repeated use of the Contents or Index.
Further evidence of the superiority of scanning the text in the linear conditions as opposed to frequent recourse to the Contents/Index in the hypertext conditions is suggested by considering the relationship between use of the string search facilities and the numbers of questions abandoned before an answer was found. Three of the questions were designed so that a string search strategy would be optimal and two of the electronic text conditions (one linear, one hypertext) supported string searching. The lack of a string search facility in the TIES condition was associated with a very high proportion of abandoned questions (58%) whilst these three questions were answered with 100% accuracy by subjects in the paper condition.
In the other two conditions in which string searching was supported it was used to different degrees of effectiveness. In the Hypercard condition the subjects employed string searching with 92% of the relevant questions and this resulted in 66% of the questions being answered correctly (and 17% being abandoned). In the Word Processor condition string searching was employed on 50% of the relevant questions and 92% were answered correctly (0% abandoned). Thus, although string searching was available to the subjects in the Word Processor condition it was used with less frequency than in the Hypercard condition. However, the subjects in the Word Processor condition answered substantially more of the questions correctly and this was presumably using strategies based on visual scanning.
Although some caution should be exercised in interpreting the results of this study, it is clear that for some texts and some tasks hypertext is not the universal panacea which some have claimed it to be. Furthermore, the various implementations of hypertext will support performance to a greater or lesser extent in different tasks. Future work should attempt to establish clearly the situations in which each general style of hypertext confers a positive advantage so that the potential of the medium can be realised.
This work was funded by the British Library Research and Development Department and was carried out as part of Project Quartet.
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