Ergonomic Criteria for the Evaluation of Human-Computer Interfaces

Authors: J. M. Christian Bastien and Dominique L. Scapin — May 1993, version 2.1 (source)

1. GUIDANCE

Definition :

User Guidance refers to the means available to advise, orient, inform, instruct, and guide the users throughout their interactions with a computer (messages, alarms,labels, etc.), including from a lexical point of view.

The criterion Guidance is subdivided into four criteria: Prompting, Grouping/Distinction of Items, Immediate Feedback, and Legibility.

Rationale(s) :

Good guidance facilitates learning and use of a system by allowing the users: to know at any time where they are in a sequence of interactions, or in the accomplishment of a task; to know what the possible actions are as well as their consequences; and to obtain additional information (possibly on demand). Ease of learning and ease of use that follows good guidance lead to better performances and fewer errors.

1.1. PROMPTING *

Definition :

As it is used here, Prompting has a broader definition than usual. Here it refers to the means available in order to lead the users to making specific actions whether it be data entry or other tasks. This criterion also refers to all the means that help users to know the alternatives when several actions are possible depending on the contexts Prompting also concerns status information, that is information about the actual state or context of the system, as well as information concerning help facilities and their accessibility.

Rationale(s) :

Good prompting guides the users and saves them, for instance, from learning a series of commands. Good prompting also allows users to know exactly the current mode,where they are in the dialogue, as well as the actions that resulted in that context.Thus good prompting helps users to navigate in the application or the system and helps to reduce errors.

Examples of guidelines:

Comments :

Prompting vs Grouping/Distinction by Format.

Prompting helps in a direct manner by suggesting to the users possible actions that may be taken. For instance, when several actions are possible (e.g., confirm, cancel,copy, etc.), only the available actions could be displayed, or indicated in a message.

Less direct means are also available to guide the users. In the above example, if all options are presented, different formats could be used to indicate those which are currently available.

When several choices or actions are possible, the most probable or most logical action can be presented in a format that distinguishes it from other options, such as a bold border encircling a push button (the default option). It is a case of Grouping/Distinction by Format, not a case of Prompting since the carriage-return option is not explicit.

Prompting consists in directly presenting the different possible actions whereas Grouping/Distinction by Format will indicate particular characteristics of these possible actions.

Prompting vs Immediate Feedback

The distinction between Prompting and Immediate Feedback is sometimes subtle.

For example, following a user action, a message can indicate that the command has been executed and also which action must be taken to continue the transaction. Thus a message can be a feedback for the previous action(s) and a prompting for the subsequent action. Immediate Feedback concerns messages that inform the user about the previous actions. Prompting concerns messages that either guide the users for future actions or suggest performing a specific action.

Prompting vs Legibility

The lexical aspects of the prompts (instructions, messages indicating to the users what needs to be done, etc.) which can have an effect on the readability (e.g., font size,type of font, etc.), concern the criterion Legibility.

Prompting vs Concision

Good prompting, such as instructions, messages indicating to the user what needs to be done may be too long. This flaw in the prompting concerns the criterion Concision. In the same way, good prompting can indicate the way data must be entered, but at the same time a problem of Concision may be introduced if, in addition to the data, the user must enter measurement units.

Prompting vs Error Protection

Error protection can be achieved by various means. Automatic mechanisms can be implemented that control the users’ inputs. For instance, after users’ entry, the computer will display an error message if the data entry format is not appropriate.This case would concern the criterion Error Protection. Another way of preventing errors would be to give users information on the type and format of the data to be entered. In this case Prompting is concerned. These two means of preventing errors can coexist.

Prompting vs Quality of Error Messages

An error message can include prompting about the means to correct errors. It is indeed a case of Quality of Error Messages, not a case of Prompting. Prompting only refers to the guidance provided to the users in error-free situations.

Prompting vs Consistency

As long as it is a matter of comparison between several transactions, objects, etc., including the ones with a prompting-oriented goal, it concerns the criterion Consistency. For instance, providing a single identification for each display in a consistent location at the top of the display frame concerns Consistency.

Prompting vs Compatibility

When the wording used for prompting differs from the users’ language, it concerns the criterion Compatibility.

1.2. GROUPING/DISTINCTION OF ITEMS

Definition :

The criterion Grouping/Distinction of Items concerns the visual organisation of information items in relation to one another. This criterion takes into account the topology (location) and some graphical characteristics (format) in order to indicate the relationships between the various items displayed, to indicate whether or not they be long to a given class, or else to indicate differences between classes. This criterion also concerns the organisation of items within a class.

The criterion Grouping/Distinction of Items is subdivided into two criteria: Grouping/Distinction by Location and Grouping/Distinction by Format.

Rationale(s) :

The users’ understanding of a display screen depends, among other things, on the ordering, the positioning and the distinction of the objects (images, texts, commands,etc.) that are presented. Users will detect the different items or groups of items, and learn their relationship(s) more easily if, on the one hand, they are presented in an organised manner (e.g., alphabetic ordering, frequency of use, etc.), and if on the other hand the items or groups of items are presented in formats or coded in ways that indicate their similarities or differences. Also, the learning and remembering of items or groups of items will be improved. The grouping/distinction of items leads to a better guidance.

1.2.1. GROUPING/DISTINCTION BY LOCATION *

Definition :

The criterion Grouping/Distinction by Location concerns the relative positioning of items in order to indicate whether or not they belong to a given class, or else to indicate differences between classes. This criterion also concerns the relative positioning of items within a class.

Rationale(s) :

The users’ understanding of a display screen depends, among other things, on the ordering of the objects (images, texts, commands, etc.) that are presented. Users will detect the different items more easily if they are presented in an organised manner(e.g., alphabetic ordering, frequency of use, etc.). Also, the learning and remembering of items will be improved. The grouping/distinction by location leads to a better guidance.

Examples of guidelines:

Comments :

Grouping/Distinction by Location vs Grouping/Distinction by Format

The grouping/distinction of items can be achieved by format and/or by location. Location and format correspond to different display features (topology vs. added graphics). For instance, menu options can be distinguished either or both with location (e.g., most frequent options at the top, less frequent options further down)and format (e.g., a line separator between a set of options concerning text layout and a set of options concerning character types).

1.2.2. GROUPING/DISTINCTION BY FORMAT *

Definition :

The criterion Grouping/Distinction by Format concerns more precisely graphical features (format, colour, etc.) that indicate whether or not items belong to a given class, or that indicate distinctions between different classes, or else distinctions between items of a given class.

Rationale(s) :

It will be easier for the user to know the relationship(s) between items or classes of items if different formats or different codes illustrate their similarities or differences.Such relationships will be easier to learn and to remember. A good grouping/distinction by format leads to a better guidance.

Examples of guidelines:

Comments :

Grouping/Distinction by Format vs Prompting

Prompting helps in a direct manner by suggesting possible actions. For instance, when several actions are possible (e.g., confirm, cancel, copy, etc.), only the available actions could be displayed, or indicated in a message.

Less direct means are also available to guide the users. In the above example, if all options are presented, different formats could be used to indicate those which are currently available.

When several choices or actions are possible, the most probable or most logical action can be presented in a format that distinguishes it from other options, such as a bold border encircling a push button (the default option). It is a case of Grouping/Distinction by Format, not a case of Prompting since the carriage-return option is not explicit.

Prompting consists in directly presenting the different possible actions whereas Grouping/Distinction by Format will indicate particular characteristics of these possible actions.

Grouping/Distinction by Format vs Grouping/Distinction by Location

The grouping/distinction of items can be achieved by format and/or by location.

Location and format correspond to different display features (topology vs. added graphics). For instance, menu options can be distinguished either or both with location (e.g., most frequent options at the top, less frequent options further down)and format (e.g., a line separator between a set of options concerning text layout and a set of options concerning character types).

1.3. IMMEDIATE FEEDBACK *

Definition :

Immediate Feedback concerns system responses to users’ actions. These actions may be simple keyed entries or more complex transactions such as stacked commands. In all cases computer responses must be provided, they should be fast, with appropriate and consistent timing for different types of transactions. In all cases, a fast response from the computer should be provided with information on the requested transaction and its result.

Rationale(s) :

Feedback quality and rapidity are two important factors for the establishment of user confidence and satisfaction as well as for the understanding of the dialogue. These factors allow the users to gain a better understanding of the system’s functioning.

The absence of feedback or a delayed feedback can be disconcerting to the user. The users may suspect a system failure and may undertake actions that may be disruptive for the ongoing processes.

Examples of guidelines:

Comments :

Immediate Feedback vs Prompting

The distinction between Prompting and Immediate Feedback is sometimes subtle.

For example, following a user action, a message can indicate that the command has been executed and also which action must be taken to continue the transaction. Thus a message can be a feedback for the previous action(s) and a prompting for the subsequent action. Immediate Feedback concerns messages that inform the user about the previous actions. Prompting concerns messages that either guide the users for future actions or suggest performing a specific action.

Immediate Feedback vs Legibility

When the quality of feedback is unsatisfactory, even from a lexical point of view, it isa matter of Immediate Feedback, not a matter of legibility. Immediate Feedback concerns all characteristics of the system’s responses following users’ actions(presence or absence of a feedback, quality of the feedback from a semantic and lexical point of view).

1.4. LEGIBILITY *

Definition :

Legibility concerns the lexical characteristics of the information presented on the screen that may hamper or facilitate the reading of this information (character brightness, contrast between the letter and the background, font size, interword spacing, line spacing, paragraphs spacing, line length, etc.). By definition, the criterion Legibility does not concern feedback or error messages.

Rationale(s) :

Performances are increased when the presentation of information on the screen takes into account the cognitive and perceptual characteristics of the users. A good legibility facilitates the reading of the information presented. For instance, dark letters on a light background are easier to read than the other way around; a text presented with mixed upper/lower case is read faster than a text presented with only upper-case letters.

Examples of guidelines:

Comments :

Legibility does not apply to feedback or error messages. Indeed, all aspects related to reading difficulties for the users, or more generally to the quality of messages concerning the feedback or the error messages should be assigned respectively to the criterion Immediate Feedback or to the criterion Quality of Error Messages.

Legibility vs Immediate Feedback

When the quality of feedback is unsatisfactory, even from a lexical point of view, it is a matter of Immediate Feedback, not a matter of legibility Immediate Feedback concerns all characteristics of the system’s responses following users’ actions (presence or absence of a feedback, quality of the feedback from a semantic and lexical point of view).

Legibility vs Quality of Error Messages

When error messages are unsatisfactory, even from a lexical point of view, it is a matter of Quality of Error Messages, not a matter of Legibility. The criterion Quality of Error Messages concerns all characteristics of information related to the users’ errors.

Legibility vs Prompting

The lexical aspects of the prompts (instructions, messages indicating to the users what needs to be done, etc.) which can have an effect on the ease of reading (e.g., font size, type of font, etc.), concern the criterion Legibility.

Legibility vs Significance of Codes

Legibility does not concern the semantic characteristics of information, their relevance or their significance. These characteristics are to be related to Significance of Codes.

Legibility vs Compatibility

The criterion Legibility does not concern the semantic characteristics of information, their relevance or their significance. When these characteristics are related to the task, then the criterion Compatibility should be considered.

2. WORKLOAD

Definition :

The criterion Workload concerns all interface elements that play a role in the reduction of the users’ perceptual or cognitive load, and in the increase of the dialogue efficiency.

The criterion Workload is subdivided into two criteria: Brevity (which includes Concision and Minimal Actions), and Information Density.

Rationale(s) :

The higher the workload, the higher the probability of making errors. Also the less users are distracted by unnecessary information, the more they will be able to accomplish their task efficiently. Besides, the shorter the required actions, the faster the interactions.

2.1. BREVITY

Definition :

The criterion Brevity concerns the perceptual and cognitive workload both for individual inputs and outputs, and for sets of inputs (i.e., sets of actions needed to accomplish a goal or a task). Brevity corresponds to the goal of limiting the reading and input workload and the number of action steps.

The criterion Brevity is subdivided into two criteria: Concision and Minimal Actions.

Rationale(s) :

Short term memory capacity is limited. Consequently, the shorter the entries, the smaller the probability of making errors. Besides, the more succinct the items, the shorter the reading times.

Also, the more numerous and complex the actions necessary to reach a goal, the more the workload will increase and consequently the greater the risk of making errors.

2.1.1. CONCISION *

Definition :

The criterion Concision concerns perceptual and cognitive workload for individual inputs or outputs.

By definition, Concision does not concern feedback or error messages.

Rationale(s) :

Short term memory capacity is limited. Consequently, the shorter the entries, the smaller the probability of making errors. Besides, the more succinct the items, the shorter the reading times.

Examples of guidelines:

Comments :

Concision vs Prompting

Good prompting, such as instructions, messages indicating to the user what needs to be done may be too long. This flaw in the prompting concerns the criterion Concision. In the same way, good prompting can indicate the way data must be entered, but at the same time a problem of Concision may be introduced if, in addition to the data, the user must enter measurement units.

Concision vs Minimal Actions

By Minimal Actions we refer here to procedures, or steps; when the length of items or data entries is concerned, then it is a matter of Concision.

Concision vs Information Density

The criterion Concision concerns the succinctness of individual items presented while Information Density concerns the density of the set(s) of information presented on the screen. Thus an item can be relevant but not presented in a sufficiently concise way. In this case the criterion Concision must be put forward. If items are superfluous then it is a matter of Information Density.

Concision vs Quality of Error Messages

The criterion Concision does not apply to error messages. When error messages are not sufficiently succinct, it is a matter of Quality of Error Messages.

2.1.2. MINIMAL ACTIONS *

Definition :

The criterion Minimal Actions concern workload with respect to the number of actions necessary to accomplish a goal or a task. It is here a matter of limiting as much as possible the steps users must go through.

Rationale(s) :

The more numerous and complex the actions necessary to reach a goal, the more the workload will increase and consequently the more probable the risks of making errors.

Examples of guidelines:

Comments :

Minimal Actions vs Concision

By Minimal Actions we refer here to procedures, or steps; when the length of items or data entries is concerned, then it is a matter of Concision.

Minimal Actions vs User Experience

The criterion Minimal Actions concerns the length of transactions and procedures, whatever the level of user experience.

When the length of transactions and procedures is inadequate for a particular user group (e.g., no short cuts are available to the experienced users), it concerns the criterion User Experience.

Minimal Actions vs Flexibility

The criterion Flexibility concerns the possibility of accomplishing a task in different ways, that is with different procedures. These procedures may be minimal or not.This criterion also concerns the means available to the users for adapting the interface to their particular needs.

Minimal Actions vs Error Correction

Problems related to the criterion Minimal Actions can result from inadequate error correction mechanisms. When the number of steps necessary to correct an error maybe reduced, it is a matter of Error Correction. The criterion Minimal Actions refers to procedures, steps or actions that are not related to the correction of errors.

Minimal Actions vs Compatibility

A lack of compatibility (e.g., inadequate match between the task and the dialogue steps) may increase the number of actions necessary to accomplish a task. In this case, the criterion Compatibility must be invoked, not Minimal Actions, which is the consequence of the problem rather than the cause.

2.2. INFORMATION DENSITY *

Definition :

The criterion Information Density concerns the users’ workload from a perceptual and cognitive point of view with regard to the whole set of information presented to the users rather than each individual element or item.

Rationale(s) :

In most tasks, users’ performances are worsened when information density is too high or too low: in these cases, errors become more likely. Items that are not related to the task should be removed.

Memory load on the user should be minimised. Users should not have to memorise long data lists or complicated procedures. They should not have to undertake complex cognitive activities when these are not required by the task at hand.

Examples of guidelines:

Comments :

Information Density vs Concision

The criterion Concision concerns the succinctness of individual items presented while Information Density concerns the density of the set(s) of information presented on the screen. Thus an item can be relevant but not presented in a sufficiently concise way. In this case the criterion Concision must be put forward. If items are superfluous then it is a matter of Information Density.

3. EXPLICIT CONTROL

Definition :

The criterion Explicit Control concerns both the system processing of explicit user actions, and the control users have on the processing of their actions by the system.

The criterion Explicit Control is subdivided into two criteria: Explicit User Action, and User Control.

Rationale(s) :

When the users explicitly define their inputs, and when these inputs are under their control, errors as well as ambiguities are limited. Moreover, the system will be better accepted by users if they have control over the dialogue.

3.1. EXPLICIT USER ACTION *

Definition :

The criterion Explicit User Action refers to the relationship between the computer processing and the actions of the users. This relationship must be explicit, i.e., the computer must process only those actions requested by the users and only when requested to do so.

Rationale(s) :

When computer processing results from explicit user actions, users learn and understand better the application functioning and fewer errors are observed.

Examples of guidelines:

Comments :

Explicit User Action vs User Control

The criterion Explicit User Action should be distinguished from User Control. The first criterion refers to the explicit character of the actions requested by the users,while the second criterion refers to the control capabilities the users should have over the ongoing processing.

3.2. USER CONTROL *

Definition :

The criterion User Control refers to the fact that the users should always be in control of the system processing (e.g., interrupt, cancel, pause and continue). Every possible action by a user should be anticipated and appropriate options should be provided.

Rationale(s) :

Control over the interactions favours learning and thus diminishes the probability of making errors. As a consequence, the computer becomes more predictable.

Examples of guidelines:

Comments :

User Control vs Explicit User Action.

The criterion Explicit User Action should be distinguished from User Control. The first criterion refers to the explicit character of the actions requested by the users,while the second criterion refers to the control capabilities the users should have overthe ongoing processing.

4. ADAPTABILITY

Definition :

The adaptability of a system refers to its capacity to behave contextually and according to the users’ needs and preferences.

The criterion Adaptability is subdivided into two criteria: Flexibility and User Experience.

Rationale(s) :

The more diverse the ways of achieving a given task, the more likely a particular user will find a way suitable to him, a way that he will master in the course of learning. It follows that different procedures, options, and commands must be available to the users for them to achieve a given goal. In addition, a given interface cannot be suitable for all its potential users. To avoid negative effects on the users, the interface must adapt to them.

4.1. FLEXIBILITY *

Definition :

The criterion Flexibility refers to the means available to the users to customise the interface in order to take into account their working strategies and/or their habits, and the task requirements. Flexibility is reflected in the number of possible ways of achieving a given goal. In other words, it is the capacity of the interface to adapt to the users’ particular needs.

Rationale(s) :

The more diverse the available means to perform a given task, the more probable the chances that users will choose and master one of them during learning.

Examples of guidelines:

Comments :

Flexibility vs Minimal Actions

The criterion Flexibility concerns the possibility of accomplishing a task in different ways, that is with different procedures. These procedures may be minimal or not.This criterion also concerns the means available to the users for adapting the interface to their particular needs.

Flexibility vs User Experience

A good flexibility should allow the general user population to adapt the interface to its particular needs. When an interface is used by several different types of users, or a particular type of users, and the interface allows users to perform a task in different ways that are tailored to their level of experience, then it is a matter of User Experience.

In other words, as soon as level of experience are invoked, the criterion User Experience is concerned.

Flexibility vs Compatibility

Flexibility may be a means for attaining compatibility; however, there can be a good flexibility without compatibility, and vice versa. For example, a form-filling display may not match the source documents, in terms of item ordering and data grouping. In this case, a problem of Compatibility should be invoked even though the interface may allow (then there is also some Flexibility) or not (then there is no Flexibility)users to modify the data entry sequence.

4.2. USER EXPERIENCE *

Definition :

The criterion User Experience refers to the means available to take into account the level of user experience.

Rationale(s) :

Experienced and inexperienced users have different information needs. It may be desirable to provide inexperienced users with prompted modes of transactions allowing simple step-by-step actions. For experienced users, computer-initiated dialogues may be boring and slow down their interactions; short-cuts may allow them to access system functions more rapidly. Different levels of interaction should take users’ experience into account.

However, most systems will have users with varying levels of experience. Users may become more expert with increased experience, or perhaps less expert after a long period of disuse. The interface should also be designed so as to accommodate the varying users’ levels of experience.

Examples of guidelines:

Comments :

User Experience vs Minimal Actions

The criterion Minimal Actions concerns the length of transactions and procedures, whatever the level of user experience.

When the length of transactions and procedures is inadequate for a particular user group (e.g., no short cuts are available to the experienced users), it concerns the criterion User Experience.

User Experience vs Flexibility

A good flexibility should allow the general user population to adapt the interface to its particular needs. When an interface is used by several different types of users, or a particular type of users, and the interface allows users to perform a task in different ways that are tailored to their level of experience, then it is a matter of User Experience.

In other words, as soon as level of experience are invoked, the criterion User Experience is concerned.

5. ERROR MANAGEMENT

Definition :

The criterion Error Management refers to the means available to prevent or reduce errors and to recover from them when they occur. Errors are defined in this context as invalid data entry, invalid format for data entry, incorrect command syntax, etc.

The criterion Error Management is subdivided into three criteria: Error Protection, Quality of Error Messages, and Error Correction.

Rationale(s) :

System interruptions caused by users’ errors have negative consequences on the users’ activities. In general, these kinds of interruptions increase the number of interactions and disturb the organisation and the accomplishment of the task. By limiting the number of errors, the number of interruptions is also limited. The performance is thus better.

5.1. ERROR PROTECTION *

Definition :

The criterion Error Protection refers to the means available to detect and prevent data entry errors, command errors, or actions with destructive consequences.

Rationale(s) :

It is preferable to detect errors before validation rather than after: the detection is less disruptive.

Examples of guidelines:

Comments :

Error Protection vs Prompting

Error protection can be achieved by various means. Automatic mechanisms can be implemented that control the users’ inputs. For instance, after users’ entry, the computer will display an error message if the data entry format is not appropriate.This case would concern the criterion Error Protection. Another way of preventing errors would be to give users information on the type and format of the data to be entered. In this case Prompting is concerned. These two means of preventing errors can coexist.

5.2. QUALITY OF ERROR MESSAGES *

Definition :

The criterion Quality of Error Messages refers to the phrasing and the content of error messages, that is: their relevance, readability, and specificity about the nature of the errors (syntax, format, etc.) and the actions needed to correct them.

Rationale(s) :

The quality of error messages promotes users’ learning of systems by indicating to the users the reasons for their errors, their nature, and by teaching them ways to prevent or solve their errors.

Examples of guidelines:

Comments :

Quality of Error Messages vs Prompting

An error message can include prompting about the means to correct errors. It is indeed a case of Quality of Error Messages, not a case of Prompting. Prompting only refers to the guidance provided to the users in error-free situations.

Quality of Error Messages vs Legibility

When error messages are unsatisfactory, even from a lexical point of view, it is a matter of Quality of Error Messages, not a matter of Legibility. The criterion Quality of Error Messages concerns all characteristics of information related to the users’ errors.

Quality of Error Messages vs Concision

The criterion Concision does not apply to error messages. When error messages are not sufficiently succinct, it is a matter of Quality of Error Messages.

5.3. ERROR CORRECTION *

Definition :

The criterion Error Correction refers to the means available to the users to correct their errors.

Rationale(s) :

Errors are less disturbing when they are easily, and immediately corrected.

Examples of guidelines:

Comments :

Error Correction vs Minimal Actions

Problems related to the criterion Minimal Actions can result from inadequate error correction mechanisms. When the number of steps necessary to correct an error maybe reduced, it is a matter of Error Correction. The criterion Minimal Actions refers to procedures, steps or actions that are not related to the correction of errors.

6. CONSISTENCY *

Definition :

The criterion Consistency refers to the way interface design choices (codes, naming, formats, procedures, etc.) are maintained in similar contexts, and are different when applied to different contexts.

Rationale(s) :

Procedures, labels, commands, etc., will be better recalled, located, recognised, and used if their format, location, and syntax are stable from one screen to the other, from one session to the next. In these conditions the computer system is more predictable,learning and generalisation are facilitated, and the number of errors made is reduced.A lack of consistency can increase the search time considerably.

The lack of consistency is one important reason for users’ rejection.

Examples of guidelines:

Comments :

Consistency vs Prompting

As long as it is a matter of comparison between several transactions, objects, etc., including instructions (prompting), it concerns the criterion Consistency. For instance, providing a single identification for each display in a consistent location at the top of the display frame concerns the criterion Consistency.

Consistency vs Compatibility

The criterion Consistency applies only within a given application. When consistency concerns external aspects (e.g., paper forms) or concerns other applications or environments, it is then a matter of Compatibility.

7. SIGNIFICANCE OF CODES *

Definition :

The criterion Significance of Codes qualifies the relationship between a term and/or a sign and its reference. Codes and names are significant to the users when there is a strong semantic relationship between such codes and the items or actions they refer to.

Rationale(s) :

When codes are meaningful, their remembering and identification are easier. In addition, non significant codes or names may lead to inappropriate users’ operations,and thus to errors.

Examples of guidelines:

Comments :

Significance of Codes vs Legibility

Legibility does not concern the semantic characteristics of information, their relevance or their significance. These characteristics are to be related to Significance of Codes.

8. COMPATIBILITY *

Definition :

The criterion Compatibility refers to the match between users’ characteristics (memory, perceptions, customs, skills, age, expectations, etc.) and task characteristics on the one hand, and the organisation of the output, input, and dialogue for a given application, on the other hand.

The criterion Compatibility also concerns the coherence between environments and between applications.

Rationale(s) :

Information transfer from one context to another is faster and more efficient when the volume of information to recode by the users is limited.

Efficiency is increased when: the procedures designed to accomplish a task are compatible with the users’ psychological characteristics; procedures and tasks are organised with respect to users’ expectations and practices; translations,interpretations, or references to the documentation are minimised.

Performances are better when information is presented in a directly usable form.

Examples of guidelines:

Comments :

Compatibility vs Prompting

When the wording used for prompting differs from the users’ language, it concerns the criterion Compatibility.

Compatibility vs Legibility

The criterion Legibility does not concern the semantic characteristics of information, their relevance or their significance. When these characteristics are related to the task, then the criterion Compatibility should be considered.

Compatibility vs Minimal Actions

A lack of compatibility (e.g., inadequate match between the task and the dialogue steps) may increase the number of actions necessary to accomplish a task. In this case, the criterion Compatibility must be invoked, not Minimal Actions, which is the consequence of the problem rather than the cause.

Compatibility vs Flexibility

Flexibility may be a means for attaining compatibility; however, there can be a good flexibility without compatibility, and vice versa. For example, a form-filling display may not match the source documents, in terms of item ordering and data grouping.In this case, a problem of Compatibility should be invoked even though the interface may allow (then there is also some Flexibility) or not (then there is no Flexibility)users to modify the data entry sequence.

Compatibility vs Consistency

The criterion Consistency applies only within a given application. When consistency concerns external aspects (e.g., paper forms) or concerns other applications or environments, it is then a matter of Compatibility.