4 Progress of purchase decision process
4.1 Phase of purchase decision
Analysis of purchase decision of consumer.
American economists and psychologist Katona characterised two types of consumer
decision :
- real decision – goods of investment character, is accompanied by :
 conscious and systematic obtaining of information about product and
 repeated comparison with competitive products,
 activity in preparation behaviour – saving or choice of other budgetary
possibilities,
 living through the future consumption.
-
addictive behaviour - subject uses – knowingly or unknowingly – previous
experiences. Usually does not go before systematic preparation of purchase. For
example :
 visit of some shops,
 relatively short decision process, influenced by actual offer situation.
Analysis show that decision process is influenced also by personal qualities. Persons
with lower IQ is the process closed sooner and it is hard to change it. Persons with higher IQ
are more opened new information and are prepared to work with them and to change
decisions.
Specific progression of activities is called purchase decision process.
Progress of purchase decision
Five main bases : problem recognising, searching for information,
alternatives, purchase decision and phase of behaviour after purchase.
valuation of
Problem recognising
- Formation of problem thanks to unfavourable change of current situation
 Damage of some device, equipment etc.
 Depletion of sources.
 Worsening of quality of marketing tools (for example changes in price).
- Formation of problem thanks to increase of level of required situation
Consumer recognises increasing of possibilities, which are connected with satisfaction
of given need : market innovations, new activities. This can also be results of consumer
thinking, cognitive learning.
Some factors of perceived relation of real and expected (required situation):
 family characteristics,
 financial deliberation, changes of conditions,
 previous decisions,
 culture,
 social stratification, individual development,
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market situations,
marketing activities,
information background and its movements.
Sometimes the purchase decision process does not develop further : contradiction is not
enough motivated, sources for its solution are not sufficient, conditions connected with
solution are too demanding for information, time etc.
Effort of marketing activation of recognising of problem can also fall contra–
productively :
- can lead to purchase of competitive product by communication stress on problem,
- purposely bigger contradiction between real and required situation can return in
form of boomerang effect at own use of product.
Searching for information
Problem recognising leads the consumer to searching for relevant information. It is
partly inner searching a partly outer searching for information.
Inner searching is reviving of appropriate information in long-term memory of consumer.
The inner searching leans on association nets of memory.
Outer searching means obtaining of information from outside.
-
First form of raised attention. Passive approach only.
Active searching represents systematic, active and pointing effort of consumer to
obtain appropriate information about possibilities to solve their problem.
- Information sources
At information obtaining :
- Sources of reference surrounding
From marketing view is valid knowledge in connection with operation of reference
groups to search for and accost ideological leaders.
- Neutral sources
Information about structure and quality of offer. Neutral sources reduce especially
risks : functional, financial and physical.
-
Sources of inner searching in sphere of marketing mix incorporate :
 personal outer sources
 non personal :
- promotional information, advertisement, scenes,
- prospects, which in general consumer gets on purchase place. Relatively
tight binding to concrete decision process,
- newspaper advertisement articles (advertoarials)
- consumer magazines
- wrappings
Disadvantage of commercial information sources is lower perceived credibility,
- Personal experience.
Among consumers exist marked differences in way of information searching, this is
important mainly from view of development of market segments profiles.
- Influences to be conditional on information searching
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Previous experience.
-
Perceived risk.
Kinds of risks :
1. Financial : releasing of too high financial amount.
2. Functional : purchased product will not fulfil expected function.
3. Physical : possibilities that product will hurt the consumer.
4. Social : worry about negative attitude of social surrounding to given
purchase.
5. Psychical : worry about possible inner conflict.
-
Market ambience.
Product characteristics.
Rate of keenness for product, problem.
Situation variables.
Predisposition of consumer.
Researches show that :
- rate of information searching falls with growing age,
- extent of information searching is higher in initial phases of family cycle,
- women have tendency to higher information searching then men,
- higher education brings bigger extent of outer information searching,
- higher social status means rather higher information searching.
Alternatives evaluation
- Choice of product type
Selective circle (set)
- Awareness set are those products, marks, which consumer recall spontaneously.
- Evoked set includes all alternatives, which consumer actively assesses by decision as
possible problem solution.
- Inner set includes those marks, consumer knows about, but they come in hi decision only
when marks of considered set are not available.
- Inept set includes marks, consumer knows about, but has negative attitude to them.
Picture No. 4 : Context of selective circle
Total offer
Not equipped set
spontaneously
equipped set
with help
evoked set
(selective active)
inert set
inept set
For marketing orientation is useful to know what create by consumer the awareness set
and evoked set. Information are obtained with help of open questions : “What marks … do
you remember ? “Do you know for example these marks …?
Howard, J.A., Sheth, J.N., The theory of Buyer Behaviour, Wiley, New York 1969
Knowledge, respecting of cognitive structures is one of essential enters in positioning or
repositioning of marks, at rebrending and strategies connected with them. In perceptual
maps appears at the same time position of competitive products.
- Own decision inside considering space
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Assumptions about fundamental things : functional attributes, symbolical
attitudes, esthetic feature, purchase criterions.
Importance given to features : used criterions have no sense for consumer.
Assumptions about products / marks
- Process of consumer decision
Two basic ways how the consumer can decide about given alternatives – non-compensatory
and compensatory rules (principles) of decision.
Non-compensatory rules of decision, evaluating of advantages in one criterion cannot
equalise absence in other criterions – disjunctive rule (principle), conjunctive rule,
lexicographic rule, elimination according to qualities.
Compensatory decision, evaluating – disadvantages in some attributes can be balanced by
advantages in other criterions.
It is additive rule : Consumer measures values of criterions at individual marks, thinks about
importance of criterions and on the base of the overall result takes out the one with the best
overall result.
It is taken out the variant with most positive attributes.
Tendency to compensation approaches breaks through more in connection with products,
where is characteristic high keenness and where number of alternatives is not high.
(D.I.Hawkins, K.A: Coney). At large number of alternatives is the procedure according to
conjunctive rule.
Hawkins, D.I., Best, R.J., Coney, K.A., Consumer Behaviour : Implications for Marketing Strategy, IRWIN 1995
- Cognitive algebra
Kroeber Riel at analysis of decision process comes out from Fishbein thesis, that it is
possible to narrow product characteristic as incentive of motivation implicite and decision
process to limited number of dominate factors.
Than the analysis is divided into these phases :
- Identification of dominant factors.
- Evaluation of importance of individual factors.
- Evaluation, how the consumer evaluates these factors at tested products.
- Synthetic evaluation of preferences in decision process.
These cognitive evaluation programmes are formalised into some schemas called “cognitive
algebra”.
Formal cognitive schemas are affected by subjective emotional influence.
At market research we meet with quasi accidental information, which can totally reverse
cognitive made decision. :
 evaluation can be by non appreciated emotions moved – misrepresented,
 schema of evaluation has tendency to move in the direction to addictive decision
processes,
 decision is from formally logical view difficult,
Factors, included in the cognitive algebra, are modified :
 for individual commodities and their role by consumer,
 for end (social) groups.
As “key” information are usually considered :
 mark
 usage
 price (one of the most problematic categories).
This approach is similar to classical economical Marshall model.
Cognitive decision programmes
 evaluating programmes :
- point systems (Engliš teleology)
- evaluating project – type Ogilvy Vademecum. (product is possible to
evaluate with some volume of percentage according to given schema).
 Selective programmes, which are based on comparative access and serves for
product selection from more alternatives.
Alternative models (accord. to Kroeber Riel) can issue from decision schemas :
- Dominate principle : subject chooses the variant, where individual signs are relative
balanced, but in one sign is the product evaluated more positively than other alternatives.
- Conjunctive principle : it is compared, accord. to Fishbein thesis, certain (limited) volume
of signs. Chosen alternative is those, which in all signs reaches certain critical value. By
conjunctive rule we meet with compensation access (is high price compensated by high
quality ?)
- Disjunctive principle : subject comes out from criterions of relatively demanding critical
values, product is chosen if reaches at least in one sign this critical value.
- Lexicographical principle : subject comes out form certain (dominant) sign, which
considers for the most important. Then he chooses alternative, which fulfil this feature (sign)
the best. Example can be decision process by fashion goods.
Kroebel-Riel W., Weinberg P. Konsumentenverhalten, Vahlen
- Principle of attribution elimination : All alternatives, which do not reach by the most
important sign certain value, are eliminated.
Some marker believes :4
- „Highly promoted goods will be good.”
- “To buy known mark is less risky”.
- “Big shops have better prices than small.”
- “New opened shops have more advantageous prices”.
- “Big package are almost always cheaper than small – per unit.”
- “New products are more expensive at introducing on market.”
- “Plastic products have less quality than from natural materials.”
Purchase decision
By evaluating of alternatives is reached purchase intent, which precedes to own purchase (or
refusal).
Social ambience in given relation we understand in narrow binding to own purchase
action. In this meaning we refer again to influence of purchase groups.
Situation influences – between important group of situation influences, which can
show up during purchase action, belong influences of business ambience.
4
accord. to Peter, J.P., Olson, J.C., Consumer Behaviour and Marketing Strategy, Homewood, IRWIN 1990
Berkovitz, E.N., Kerin, R.A., Rudelius, W.. Marketing, 2 nd ed., Homewood, IRWIN 1989
Picture No. 4-2 : Purchase decision
attitudes of others
evaluating of alternatives
purchase intent
situation factors
purchase decision
perceived risk
- Situation influences of business ambience
- Assortment.
- Merchandising : mean (mostly) way of goods exhibit (in shop).
- Atmosphere in shop : outer and inner elements
- Personnel : social aspects, expertise, purchase qualification – specific event of
marketing research - mystery shopping.
Analysis - decision tree
Analysis of cognitive decision programme is part of analysis called decision tree.
In analysis decision tree we look for how individual phases, elements of decision
process follow on time continuous. Analysis includes :
-
phase of information collecting : has different rate of activity in dependence with
real or addictive decision
-
phase of choice of purchase place : connected with segmentation analysis,
phase of activities in decision process : it is important the sequence of purchase
decisions,
phase of choice : how and where happens choice of commodity, mark, product,
phase of choice criterions : accord. to above stated schemas.
Respondent is not able to describe in detail his decision process, therefore it is necessary to
proceed :
- good preparation of phasing,
- pair comparison of individual phases,
- analysis of concrete events.
Methodology of analysis decision tree requires elaborated questionnaire, as specific
methodological process is used so called assist purchase, respondent is accompanied by
questioner during shopping and describes his thoughts and justifying why he is doing
individual operations.
Decision tree analysis is important for placing of promotions (appeals) to a place or
media.
- Purchase decision – Finish of purchase action
 Purchase of certain product – alternative of purchase decision or decision from
other alternative.
 Postponement of purchase – missing of confirmation about right decision or short
time of postponement.
 Refusal of purchase. (to use other means – repair)
After purchase behaviour
The last phase starts with usage of product.
Picture No. 4-3 : Behaviour after purchase
loyalty
generalisation
positive word-of-mouth
yes
Usage Expecting
satisfaction ?
no
change of mark
discrimination
negative W-o-M
Satisfaction is not only result of usage of product, but is also connected with level of
expectation.
Expectation is changeable in time.
- Dimensions of satisfaction / dissatisfaction
It is useful to follow series of partial levels :
 Satisfaction with functional characteristics of product quality, appearance,
symbolic, social and purchase characteristics and others.
 Satisfaction with other marketing activities.
 Importance given to characteristics.
 Potential changes in behaviour.
 Connection with purpose of product usage.
 Average satisfaction in given market area, individual satisfaction and difference in
satisfaction in market segments.
- Factors strengthen satisfaction
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product, which solves problem in required way,
corresponding communication about product character,
good information,
good service, after purchase services,
responsive approach to tools of shop support,
marketing based on relationships (relationship marketing)
dissatisfaction with competition.
- Factors strengthen after purchase dissonance and dissatisfaction
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consumer must decide among more equivalent alternatives,
it is not possible to try the product,
there is a big spontaneity of purchase,
small possibility to cancel the purchase (return the product, change for others etc.)
consumer has few information about product,
consumer is satisfied with competition offer,
consumer´s characteristics are indecisiveness and low self-assurance.
- Importance of satisfaction with product, purchase decision
Satisfaction with product is the base of marketing concept and has basic importance.
- Loyalty (brand loyalty, producer)
- is intentional (non-accidental),
- continues in time,
- is based on choose of alternatives,
- is function of psychological (evaluating) process.
- Generalisation : Consumer his satisfaction from good experience transmits to
advantageous incline to given company at purchase decision and to its products.
- Positive “Word-of-Mouth”. Satisfied consumer acclaims product, mark in his
personal communication with other members of his reference groups.
- Consequences of dissatisfaction
Dissatisfaction leads to change of mark, discrimination and negative references.
- Change of mark (brandswitching) : Consumer decides for other product.
- Discrimination. Consumer does not buy any product from this firm.
- Negative “Word-of-Mouth”. Consumer hands over his negative experience to other
members of his reference groups.
- Products laying aside
Consumer after some time can decide to eliminate a product from usage. The product
can be laid aside : (See picture No. 4-4) :
 partially – in frame of multiply furnishings (second habitation, reserve)
 parted with,
 exchanged,
 sold.
Picture No. 4-4 : Variants of product laid aside :
eliminate from usage
to keep
other purpose
of use
to weed out temporarily
deposit
rent
lend
to weed out permanently
give
sell
change throw away
The way how the product consumers do not use any more has clear marketing implications :
 connection with environment
 possibilities for recycling
 marketing inputs in level of offer new for old.
Following of laid aside process offers often interesting insight on consumers
behaviour.
 It is possible to affect segments responsive to environmental problems.
4.2. Modification of purchase decision process
Routine, accustomed purchase behaviour – by purchase of goods, which consumer
knows, which buys frequently, which is not connected with a big risk.
Limited problem solution - occasional purchase when consumer knows given
product category, but decides between not tested products.
Enlarged decision – articles, products with low purchase frequency, with high price,
big perceived risk.
- Factors influencing integration of type of purchase decision
Table No. 4-1 : Circumstances of integration of type of purchase decision
Problem solution
Direction of influence
routine
limited
complex
frequency of purchase
price
high
low
average
average
low
high
keenness
knowledge about product
perceiving risk
information searching
decision rule
low
high
low
very limited
impulse, habit,
routine
restrained
lower
lower
limited
noncompensatory
high
low
high
intensive
compensatory
Arnould, E.J., Price, L., Zinkhan, G.M., Consumer, McGraw-Hill/Irwin, 2 ed. 2004, p.805
Solomon, M.R., Consumer Behaviour, Needham Heights, Allyn and Bacon 1992
- Keenness (involvement) and purchase decision
Process of purchase decision if significant influenced by involvement. We ca
differentiate purchase involvement and product involvement.
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-
Purchase involvement – level, how the consumer deals with purchase decision
and involvement. Rate of purchase involvement is temporary condition of
consumer´s mind.
Product involvement means permanent consumer´s interest in given product
category. This involvement must not be connected with purchase of product.
Consumer can be with his purchase little involved - because he uses only the one
and no other mark.
Table No. 4-2 : Factors of involvement
Factors of involvement
High involvement
Low involvement
value of product for consumer
stability of interest
risk
emotional experience
relation to group norms
information obtaining
learning/ qualifying
getting use to
searched level of needs satisfying
mark evaluation
big
permanent
big
high
express norms
active
cognitive
more assimilation effect
optimal
before purchase
small
occasional
small
low
do not express
accidental, passive
classic
more contrast effect
sufficient
after purchase
On basis of involvement and offer structure are described 4 categories of purchase decision
process – Assael nut – see Picture No. 4.5.
- Influence of rationality / emotion on KRP process
High or low involvement for purchase is not fully associated with rational or emotive
position of decision.
It is about two parallel developing courses of consumer´s purchase decision.
Picture No. 4-5 : Sorts of purchase decision according to H.Assael :
High involvement
Low involvement
Big differences between
alternatives
Complex purchase
decision
Purchase behaviour
looking for varieties
Small differences between
alternatives
Purchase behaviour
lowering dissonance
Habit purchase
decision
- Complex purchase decision
With integrating of all phases of purchase decision into involvement process we meet
in following situations :
 articles with high prices,
 technically complicated products, things of long-term use,
 articles with high (perceived) risk of use (medicaments, cars),
 articles with higher symbolical value (clothes).
Assael H, Consumer Behaviour and Marketing Action, 4th ed., Boston, PWS-Kent Publishing Company 1992
Here we meet most often with realistic occurrence of compensation rules of decision.
By these processes has bigger importance after purchase dissonance. Effort to low
dissonance is also so called assimilation effect. Consumer accustoms with product, e.g.
ignore (and relativizes) some insufficiency of product and estimates its merits.
When occur big disagreement between expected and concrete functions of product,
appears conversely contrast effect – it leads to domination of negative features at evaluating
of purchased product and later to refusal of this mark at all.
purchase decision process with symbolic sense :10
- Considerable importance have emotional factors, criterions.
- Product is bought rather for its symbolic than utility – function value.
- Importance of self-conception and social roles in KRP.
- Less – explicit – direct expressing of utilities : who uses given product, mark, who
agrees it. Esthetical feelings.
- Less – rational features, or product characteristics (function parameters, price)
- Routine – habit purchase decision
Is repeated purchase decision, doing almost without searching for information and
evaluating of variants. Own decision is almost missing.
Routine purchase is connected with low involvement. Loyalty to mark can influent
from originally complex decision. By repeated purchase is not choice of mark from
consumers view important, purchase is not capital-intensive, no risk. When a problem
appears, for its solution is given product essential, consumer buys the best accessible mark,
which he to can accustom to buy (without previous alternatives evaluation).
In consumer´s view has habit purchase its importance. Lower risks (if any). Therefore
buys often mark, that buy others. Saves time and spends effort, minimises necessity to look
for new information.
10Hirschman,
E.C., Holbrook, M.B., “Emerging Concepts, Methods, And Propositions”, Journal of Marketing, Summer 1982
- Impulsive purchase behaviour
This purchase behaviour is characteristic by often changes of marks (brandswitching).
4.3. Diffusion of innovations
Consumers in his relation to new product, which finally starts to use, goes through
some stages :
- Adoption process
1. Knowledge.
2. Understanding.
3. Interest.
4. Evaluation, substantiation.
5. Attempt.
6. Adoption.
- Diffusion process
Four main positions of diffusion of innovations :
 character of own innovation., (discontinuous, dynamic continuous,
symbolic continuous,
 communication ways (positive w-o-m, use of co-branding, use of content
complementary www),
 conditions of social system – relation inside reference groups and between
them, importance of specific norms, traditions, standards, opinions
expected inside social system,
 time.
Loudon, D.L., DellaBitta, A.J., Consumer Behaviour : Concepts and Applications, 4 th ed., McGraw Hill 1993, adapted
Diversity of consumers in willingness to adopt new products is intercepted in few
groups (E.M.Rogers) :
-
-
Innovators. Buy product as first, consumer radicals. (2,5 % of population).
Early adopters. Belong between consumers who are very opened to new products,
consumer liberals. (13,5 % of population).
Early majority. Adopt new product earlier then average consumer, they like new
products, but their relation is more careful. (approx. 34 % of population of given
market).
Late majority. Buy product or start to buy regularly only when the product use
many people in his surrounding. Conservative consumers. (further 34 % of given
market).
-
-
Laggards. Adopt new product when everybody has it or buys it. From view of
market it is not a new product anymore. Consumers ultraconservatives. (Last 16 %
of consumers).
Not accepted. They never buy given product from different reasons.
Stated groups of consumers can difference according to product categories. We meet
similar problem as by opinion leaders (opinion leaders also appear especially among
innovators and early adopters).
- Influencing affecting diffusion and adoption
Process of propagation of innovations among consumers influence some fundamental factors:
 Type of decision. Collective or individual. The less persons is integrated, the
slower the innovation spreads.
 Relative advantage. The more advantageous than current problems solutions is the
innovating perceived, the faster spreads (fax, digital cameras).
 Satisfying of feeling needs. The clearer and more important needs the innovation
satisfies, the faster spreads. (Example use of Pampers).
 Observability, visibility, communication. If effects are positive, effects of new
product visible, the product spreads better. (Example spreading of walkmen and
mobile telephones).
 Difficulty. The more difficult to understand usage, purpose, the more difficult is
usage, the slower in the innovation spread.
 Compatibility. The more marked changes at complementary products requires the
innovation, the slower it spreads.
 Possibility to try. The better is possibility to try the product (example low price),
the faster it spreads. With this is connected also partibility – possibility to buy
little amount, this supports willingness to try the product.
 Perceived risk. The lower, the faster in innovation diffuse.
 Values barriers. Unknown relation price/value (value for money). Innovations
have often relatively high prices. Consumer cannot by such innovations, where is
no comparison and experience, adequately at his purchase decision justify higher
price.
 Character of social category, group. Changes adept rather categories, groups of
younger, more educated.
 Psychological barriers . Connected with tradition and image.
 Marketing effort. When appropriately spent means on marketing communication
and other parts of marketing mix, the innovation spreads faster.
Rogers, E.M., Shoemaker, F., Communication of Innovations, Free Press, New York 1971
4.4 Situation conditional
Situation influences are all factors, that do not eventuate from consumer´s
predisposition and that is not possible to understand as impulses producing some consumer
behaviour, but at the same time they influence him.
Most of situation influences on consumer behaviour is possible to place in one of
following groups :
- Physical circumstances :
For example change of weather and other natural events, change of physical ambience
of shops, geographical elements and places of institutions.
- Social circumstances :
It is about other persons present at consumer´s decision in all its phases. This way
influence consumer behaviour of individual people, who are not members of social groups of
consumer. These accidental social interaction, are form of “Word of Mouth”, in this case is
reference power lower.
- Time circumstances :
Categorisation of consumer behaviour in certain time scope, that has few levels :
- Seasonality,
- events in past and in the future,
- time necessary fore concrete activity,
- time to disposal – not only time for purchase, but also time of preparation and
usage.
- Type of task :
Specific argument of purchase or opportunity of usage, information obtaining,
binding to specific role. Different connections of purchase for yourself and purchase for
others (example present).
- Previous conditions :
Momentary disposition of consumer (anxiety, pleasure, excitement,…), momentary condition
of consumer, financial situation.
Belk, R.W., “Situational Variables and Consumer Behaviour”, Journal of Consumer Research, December 1975
- Others non expected changes of ambience.
For example : changes in traffic, in shop nests and services (goods takeover, different
temporary closures, adaptation, changes in personnel), other changes in infrastructure (current
is not on,…).
In connection with affecting on situation influence develop following tendencies :
 The bigger is mark loyalty, the less important is affect of situation
influence.
 The bigger is permanent product involvement, the smaller is affect of
situation influence.
 Multiplied usage of product reduces level of situation influence.
Theme to think over :
1. Situations leading to problems in case of ski equipment, box of chocolates, video.
2. Factors influencing the level of required and real situation in case of jeans and in case of
siting sets. To persuade about propriety of your hypothesis. How to integrate this into
marketing approach ?
3. Can social and psychological risk influence searching of information, connected with
decision of purchase of washing machine. If yes, how ?
4. Why wrapping of articles of long term usage are not used very often by information
searching.
5. Example of heuristic abbreviation at choice of variants.
6. When and under what conditions is usable approach that after purchase disonance can be
lower by warning on limits, which has given product at problems solution.
7. For which type of purchase decision are most suitable prospects and why.
8. What way of marketing communication is important at orientation to keep habit decision.
9. Which tools are used at orientation for searching variables ?
10. Choose some of yours own purchase action. Estimate effect of situation influence on your
consumer behaviour.
11. What communication appeals you use for stragglers on car market.
12. Possible diffuse barriers in case of products : encyclopedia on CD ROM, - solar heating, trip to heart of Africa.
Literature
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Arnould, E.J., Price, L., Zinkhan, G.M., : Consumers, McGraw-Hill/Irwin, 2 ed.
2004, ISBN 0-07-253714-0
Assael, H., Consumer Behaviour and Marketing Action, Boston, PWS-Kent
Publishing Company 1992, ISBN 0-534-02990-6
Berkowitz, E.N., Kerin, R.A., Rudelius, W., Marketing, 2nd ed., Homewood,
IRWIN, 1989, ISBN 0-256-07513-1
East, R..: Consumer Behaviour, Advances and Applications in Marketing, Prentice
Hall Europe, 1997. ISBN 0-13-359316-9
Hanna, N., Wozniak, R., Consumer Behaviour : An Applied Approach, , Prentice
Hall, 2001. ISBN 0-13-089502-4
Hawkins, D.I., Best, R.J., Coney, K.A. : Consumer Behaviour : Implications for
Marketing Strategy, 6th., IRWIN 1995, 0-256-16547-5
Koudelka J., Spotřební chování a marketing. Praha, Grada 1997. ISBN 80-7169372-3
Mühlbacher, H., Selektivní propagace, BaB, Praha 1993. ISBN 80-901444-6-2
Underhill, P., Proč nakupujeme , Praha, Management Press 2002. ISBN 80-7261055-4