Costs for correcting errors. Analytical evaluation. Performance measurement. Empirical evaluation GOMS. GOMS model. Let users try out a prototype

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1 Why ad how? Usability aalysis ad ispectio Why? Iterative desig Prototypig Measurig usability Objective/subjective feedback Quick ad dirty Slow ad clea With or without users Evaluatio Questios that might arise durig systems developmet: Will the switch board operator be able to aswer more telephoe calls per hour tha before? Will less customers have problems withdrawig cash from the ATM? If a user eters a wrog umber, what is the cosequece ad ca we recover from it? Evaluatio Evaluatig usability These questios are about usability Usability ca be measured through such questios Evaluatios typically address whether the system meets the requiremets, it seldom explais the reasos behid the problems. ca we chage the curret meu structure without causig problems? how fast ca the users read text from the scree? how log time will it take to fid specific iformatio decreasig the fot size from 12 p to 10 p, what cosequeces will it have? how small ca we make the buttos? Measurig usability No silver bullet Evaluatio durig the developmet,ot afterwards usability is ot oly a measure but a goal for developers ad developmet. Usability builds o aalysis ad experimets. Iexperieced developers ofte igore validatio i preferece of verificatio of a system. 1

2 Costs for correctig errors Costs Time sice project start Aalytical evaluatio A logical simulatio of user behaviour E.g. GOMS, KLM, Cogitive Walkthrough Ca be used to test thigs before they have bee built. Saves time sice we do ot eed to costruct i advace. No user experimets ecessary. Create a sequece of steps ad measure the time per step. Empirical evaluatio Let users try out a prototype Simple ad cheap tests. Performace measuremet Test users perform predefied tasks Defie a set of usability goals Measure errors ad times Laboratory + Results i hard umbers, easy to compare + Objective results - time cosumig, expesive - skilled users for skilled performace GOMS Measurig speed of performace Describes differet possible ways (sequeces) of solvig a problem Goal - a certai objective to be achieved Operator - available actios Methods - Sequeces of operators Selectio rules - whe choosig betwee methods GOMS model GOAL: PHOTOCOPY PAPER GOAL: LOCATE-ARTICLE GOAL: PHOTOCOPY-PAGE repeat util o more pages GOAL: ORIENT-PAGE OPEN-COVER SELECT-PAGE POSITION-PAGE CLOSE-COVER GOAL: VERIFY-COPY LOCATE-OUT-TRAY EXAMINE-COPY GOAL: COLLECT-COPY LOCATE-OUT-TRAY REMOVE-COPY (OBS! Yttre målet fullföljt!) GOAL: RETRIEVE-JOURNAL OPEN-COVER REMOVE-JOURNAL CLOSE-COVER 2

3 Keystroke-Level Aalysis Divide each task-performace ito compoets assig executio times to each compoet e.g. press key s, poit with mouse s + compare differet methods - oly o smaller parts of the work KLM model Operatio Amärkig Tid (i sekuder) K Tryck ed taget Good maskiskrivare (90 ord/mi.) 0,12 Medelmåttig maskiskrivare (40 ord/mi.) 0,28 Icke-maskiskrivare 1,20 B Muskappstryckig er eller upp 0,10 dubbelklick 0,20 P Peka med muse Fitts lag 0,1log(D/S+0,5) Medelrörelse 1,10 H Had till eller frå tagetbord 0,40 D Rita (domäberoede) - M Metalt förbereda sig 1,35 R Respos frå systemet - Tabell X: tider för vissa operatioer som e operatör utför eligt KLM-metode (efter Card, Mora & Newell, 1983) KLM example Exempel. Det fis två olika sätt att utföra kommadot Spara. Atige ka ma välja Ctrl-S som e tagetkombiatio på tagetbordet, eller också ka ma välja alterativet spara i arkivmey. Alterativ 1: Ctrl S T 1 = M + H + K = 1,35 + 0,40 + 0,28 = 2,03 sek Alterativ 2: Meyalterativ T 2 = M + H + P + B + P + B = 1,35 + 0,40 + 1,10 + 0,10 + 1,10 + 0,10 = 4,15 sek Thikig aloud users verbalise their thoughts idetify miscoceptios of the system + direct feedback from the users - ot atural to thik out loud - difficult to verbalise their decisios Questioaires Subjective satisfactio + Ca be distributed to may people - Users aswer what they thik they do, ot what they actually do Cogitive Walkthrough A evaluator walks through the iterface Tries to act as a user Actios based o kowledge about users + Quick - Dirty - Does ot ivolve users, difficult to capture domai specific problems 3

4 Cogitive walkthrough Explaatory learig Costructed for ovice users Suitable for walk-up-ad-use-iterfaces A successive walkthrough of tasks based o questios o differet levels Does the user see the search alterative? Do the user select the right alterative? Do the user uderstad the system respose? Card Sortig Physical paper cards with text ad images The test perso sorts the cards accordig to importace Good for sortig icos, cocepts etc. Ca promote uderstadig ad relevace of cocepts by users Requires real users for good results Heuristic evaluatio Uses sets of guidelies Ispectio of the iterface Documet potetial usability problems + Easy to apply + possible to use early i the desig - Domai problems Heuristic evaluatio Jacob Nielse, Measures usability Iformal walkthrough Cheap ad simple No users required, ca be performed idividually, requires miimal plaig, ca be used early i the process Cocetrates o idetifyig errors i the desig (good ad bad) Heuristic evaluatio method A group of evaluators (more evaluators fid more errors) 3-5 persos Desig help i the ispectio Heuristic evaluatio 1. Simple ad atural dialogue 2. Speak the users laguage 3. Miimise Users Memory Load 4. Cosistecy 5. Feedback 6. Clearly marked exits 7. Shortcuts 8. Good error messages 9. Prevet errors 10. Help ad documetatio 4

5 Simple ad Natural dialogue Obvious how to iteract with the system Groupig of objects Eough iformatio o the scree Overview ad details Avoid cofusig decoratio Speak the users laguage Domai laguage Avoid system or computer laguage Use metaphors familiar to the users Icos, pictures, etc., relevat for the domai Miimise user memory load Eough iformatio o the scree Recogitio istead of recall Highlight importat iformatio Show status iformatio Default values Cosistecy Cosistet layout Cosistet iteractio Cosistet laguage Cosistet fuctioality Feedback Show waitig times Feedback for actios Work related feedback System failure Clearly marked exits Show the way the user has walked through the system How to get back ad forward Orieted i the iformatio space 5

6 Shortcuts Use shortcuts to perform actios Type ahead Jumps to a desired locatio Reuse of iteractio history Good error messages Avoid obscure data code A error No 13 has occurred Use the users laguage Prevet error Dialogues for actios that may lead to serious cosequeces Avoid modes Show status Support udo ad redo Help ad documetatio Mauals should ot be ecessary Give o-lie help o the users iitiative If o other solutio is possible, give help at the iitiative of the system Nielse s ew desig Visibility of system status The system should always keep users iformed about what is goig o, through appropriate feedback withi reasoable time. Match betwee system ad the real world The system should speak the users laguage, with words, phrases ad cocepts familiar to the user rather tha system-orieted terms. Follow real-world covetios, makig iformatio appear i a atural ad logic order Nielse s ew desig User cotrol ad freedom Users ofte choose system fuctios by mistake ad will eed a clearly marked emergecy exit to leave the uwated state without havig to go through a exteded dialogue. Support udo ad redo. Cosistecy ad stadards Users should ot have to woder whether differet words, situatios, or actios mea the same thig. Follow platform covetios. 6

7 Nielse s ew desig Error prevetio Eve better tha good error messages is a careful desig which prevets a problem from occurrig i the first place. Recogitio rather tha recall Make objects, actios ad optios visible. The user should ot have to remember iformatio from oe part of the dialogue to aother. Istructios for use of the system should be visible or easily retrievable wheever appropriate. Nielse s ew desig Flexibility ad efficiecy of use Accelerators usee by the ovice user may ofte speed up the iteractio for the expert user such that the system ca cater to both iexperieced ad experieced users. Allow users to tailor frequet actios. Aesthetic ad miimalist desig Dialogues should ot cotai iformatio which is irrelevat or rarely eeded. Every extra uit of iformatio i a dialogue competes with the relevat uits of iformatio ad dimiishes their relative visibility. Nielse s ew desig Help users recogise, diagose ad recover from errors Error messages should be expressed i plai laguage (o codes), precisely idicate the problem, ad costructively suggest a solutio. Help ad documetatio Eve though it is better if the system ca be used without documetatio, it may be ecessary to provide help ad documetatio. Ay such iformatio should be easy to search, focused o the user s task, list cocrete steps to be carried out, ad ot be too large. Heuristic evaluatio Not suitable for repeated aalysis (with the same perso). Ca be solved by rotatig the ispectio tasks Good results if the evaluators are skilled Good i combiatio with real user testig (the techiques complemet oe aother) Gradig the errors 0 I do ot agree that this is a usability problem at all 1 Cosmetic problem oly 2 Mior usability problem: should be give low priority 3 Major usability problem: importat to fix, so should be give high priority 4 Usability catastrophe: imperative to fix this before product ca be released How to use the results Aalyse the results Idetify solutios to the problems Create a ew prototype Optimisig betwee requiremets 7

8 Formative evaluatios Helps formig the system Iterative testig Summative evaluatio tests the etire system i the ed (whe it is too late to do aythig) Formative evaluatios Experiece teaches you to build prototypes ad to make cocrete decisios Iformal user tests with simple prototypes measures errors early ad simple. Field tests with prototypes with a series of chages to measure differece i preferece, error rate, speed, etc. Cotrolled experimets (all importat parameters are uder cotrol) Evaluatio steps Idetify usability aspects, specify special requiremets o the product Produce a prototype Prepare experimets (Fid users, select parameters to test, documetatio method) Test ad collect data Aalysis Coclusios Evaluate... Which method should you use ad why? Micro wave ove - which is the fastest way of heatig your food, 1.10 or 1.11? System for phoig via your computer. Public service phoe (e.g. Bak, RSV) Web site for fidig courses (e.g. Aske) Digital wrist watch with oe butto 8