Housing and Interior Design II: Energy as a Resource, Product Design, Ergonomics and Work Study, Furniture and Furnishings, and Research Tools, Scales, Reliability and Validity

Design thinking is a human-centred process for solving problems, often set out in five stages: empathise (understand the users and their context), define (state the problem from their point of view), ideate (generate many possible solutions), prototype (build quick, cheap models) and test (try them with users and learn). The stages loop back rather than run in a line. The UK Design Council's Double Diamond (2005) describes the same idea as two cycles of opening out and narrowing down: discover and define, then develop and deliver. A new product spreads through a population as a diffusion of innovation; Rogers found that adoption is faster when the product offers a relative advantage, is compatible with existing values and practices, is not too complex, can be tried on a small scale and has visible results.

• Design communication moves an idea to others: sketches, orthographic and isometric drawings, renderings, mood boards, storyboards, CAD models, physical models and prototypes, and presentations.
• Ergonomic considerations: fit the product to its users' body dimensions, strength and reach; make controls easy to see, understand and operate; reduce effort, awkward posture and repetition; design for safety and for errors that can be recovered from.
• Universal design, whose seven principles were set out at North Carolina State University in 1997, aims at products usable by all people without adaptation: equitable use, flexibility in use, simple and intuitive use, perceptible information, tolerance for error, low physical effort, and size and space for approach and use.

Ergonomics (human factors) is the scientific discipline concerned with understanding interactions among humans and the other elements of a system, and applying that knowledge to design so as to optimise well-being and performance. Its significance in Home Science is that household work, much of it done by women, is real physical work in workplaces that were rarely designed for it. Its scope covers physical ergonomics (posture, loads, repetitive movements, workplace layout), cognitive ergonomics (perception, memory, mental workload, decision making) and organisational ergonomics (work schedules, teamwork). It studies the person-machine-environment system: the worker, the tools and equipment, and the surroundings of heat, light, noise and space, as interacting parts.

• Anthropometry supplies body dimensions, static (structural, measured at rest) and dynamic (functional, measured during movement, such as reach). Designs use percentiles: clearances (door heights, knee space) are set for the large user (95th percentile) so almost everyone fits; reaches (shelf heights, control positions) for the small user (5th percentile) so almost everyone can reach; where possible, adjustability covers the range; designing for the average fits few people well.
• The physiological cost of work rises with the load and pace of work, awkward or static posture, poor methods and tools, a hot, humid, noisy or ill-lit environment, the worker's age, sex, fitness, nutrition and health, the length of work and the lack of rest. It is measured by the rise in heart rate above resting, by oxygen consumption and by energy expenditure; one litre of oxygen consumed corresponds to about 5 kcal of energy.
• Body mechanics: keep a wide base of support, bend the knees rather than the back, hold loads close to the body, avoid twisting while lifting, push rather than pull, use the large muscles, and change posture often.
• Functional design of the workplace: work surfaces a little below elbow height for most standing tasks (lower for heavy work such as kneading, higher for fine work), frequently used items stored between shoulder and hip height within the normal reach area, adequate knee and toe space, good light on the task, and a sequence of work centres that follows the flow of work.

Time and motion study analyses how work is done in order to improve it. Frederick W. Taylor pioneered time study with the stopwatch; Frank and Lillian Gilbreth developed motion study, breaking work into basic motions they called therbligs, and Lillian Gilbreth applied it to the kitchen. Tools include process charts using standard symbols (operation, transport, inspection, delay, storage), flow and string diagrams, and filmed micromotion analysis. In time study, normal time = observed time × performance rating / 100, and standard time = normal time plus allowances for rest and personal needs: a task observed at 2.0 minutes by a worker rated at 110 per cent has a normal time of 2.2 minutes, and with a 10 per cent allowance a standard time of 2.42 minutes. Energy studies measure the energy cost of tasks by indirect calorimetry (oxygen consumption, with respirometers) or by heart rate monitoring.

• Wall finishes: lime wash and distemper (cheap, less washable), water-based emulsion paints, oil-based enamel (washable, for kitchens and doors), texture paints, wallpaper, wood or laminate panelling, tiles and stone cladding, exposed brick.
• Windows: casement, sliding, sash (double-hung), pivoted, louvred, bay, picture, clerestory and French windows; they admit light and air, frame views and shape the room's character.
• Window treatments are hard (Venetian, vertical, roller and Roman blinds, shutters) or soft (sheer and café curtains, draperies, with valances, pelmets, swags and tiebacks). Curtain fabric is calculated for fullness: the finished width is usually about 1.5 to 3 times the window width, commonly double. For a 1.5 m window at double fullness, 3.0 m of width is needed; with fabric 1.2 m wide that is 3.0 / 1.2 = 2.5, rounded up to 3 widths, each cut to the finished length plus allowances for hems and heading.

Once the sample is chosen (chapter 12), data are collected with tools, which must be selected and prepared to measure the study's variables. A questionnaire is a set of questions answered by the respondents themselves, in print or online; it is cheap for large, literate samples, but response rates can be low. A schedule is a similar form filled in by the investigator in a face-to-face interview, suited to respondents who cannot read. Questions are open or closed (dichotomous, multiple choice, rating), and every tool is pilot-tested to find unclear or leading items. Interviews may be structured, semi-structured or unstructured, individual or in focus groups. Observation may be participant or non-participant, structured (with checklists or rating scales) or unstructured, and natural or controlled.

Reliability is the consistency of a tool. Test-retest reliability correlates scores from two administrations (stability); parallel-forms reliability correlates two equivalent forms (equivalence); split-half reliability correlates two halves of one test and corrects the result to full length with the Spearman-Brown formula, r = 2r_half / (1 + r_half), so a half-test correlation of 0.6 gives 1.2 / 1.6 = 0.75; internal consistency is estimated by Cronbach's alpha (0.70 or more is usually acceptable) or, for right-wrong items, Kuder-Richardson formula 20; inter-rater reliability checks agreement between observers, for example with Cohen's kappa. Validity is the extent to which a tool measures what it claims to measure. Content validity asks whether the items cover the domain (face validity is its superficial form); criterion validity compares scores with an external criterion measured at the same time (concurrent) or later (predictive); construct validity asks whether scores behave as the theory predicts, converging with related measures and diverging from unrelated ones. A tool can be reliable without being valid, but not valid without being reliable.