age, period, or birth cohort: what determines demographic differences in seafood consumption?...

Age, Period, or Birth Cohort: What Determines Demographic

Differences in Seafood Consumption?

Joachim ScholdererMAPP, The Aarhus School of Business,

Denmark Eiliv Lund

Institute of Community Medicine, University of Tromsø, Norway

Torbjørn TrondsenNorwegian College of Fishery Science, University of Tromsø,

Breivika, Norway

www.fishmarketing.com

IIFET 2002, 15.08.02. www.fishmarketing.com

T. Trondsen. Age, cohort and period. 2

Background

• Earlier studies:– H1: Young people consume less fish than older people

• Prognosis: less consumption in future

– H2: People increases fish consumption as they grow older

• Prognosis: Fish consumption do not decrease even if young people now a day consume less fish than earlier generations

• Increasing elderly population: consequences for seafood consumption?



Aim of study

• The aim of the present study was to separate the effects of “age” on fish consumption– as a cohort effect– a period effect– an effect of biological ageing



Possible implications of the underlying cause

If cohort a general ageing of society would imply decreasing

consumption levels over time as older, high-consumption cohorts are dying away

If period increase or decrease over time would depend on the

existence and shape of a general trend

If biological age– the ageing of society would imply increasing

consumption levels over time



Observed means seafood dinners per month

Fat fish Lean fish Processed fish

Birth year

1996 2001 % change

1996 2001 % change

1996 2001 % change

1951-1955

2.3 2.5 6.9 4.4 3.6 -17.2 3.0 4.4 46.5

1956-1960

1.8 2.3 26.2 4.0 3.4 -15.6 3.2 4.6 44.5

1961-1965

1.9 2.0 8.2 3.8 3.2 -16.3 3.2 4.8 47.6

1951-1965

2.1 2.3 8.5 4.1 3.4 -16.4 3.1 4.6 46.2



Methods• Panel data from the Norwegian Women and Seafood

Consumption Study (NOWAC)• Cohorts selected women born 1951-1966• Survey questionnaires mailed to a stratified random

sample from the Norwegian population registry in 1996 and 2001

• Representative for the female Norwegian population• Complete data sets for both periods were obtained

from N = 4590 respondents• Data analyzed by means of multivariate linear models



Results: Cohort effects

0.0

1.0

2.0

3.0

4.0

5.0

6.0

1950 1955 1960 1965

Consumption of fat fish(Number of meals per month)

Period = 2001

Period = 1996

0.0

1.0

2.0

3.0

4.0

5.0

6.0

1950 1955 1960 1965

Consumption of lean fish(Number of meals per month)

Period = 2001

Period = 1996

0.0

1.0

2.0

3.0

4.0

5.0

6.0

1950 1955 1960 1965

Consumption of processed fish(Number of meals per month)

Period = 2001

Birth cohort

Period = 1996

F i g u r e 1 . L i n e a r e f f e c t s o f b i r t h c o h o r t o n c o n s u m p t i o n o f f a t , l e a n a n d p r o c e s s e d f i s h w i t h i n c o n s u m p t i o n p e r i o d s 1 9 9 6 a n d

2 0 0 1 .

1996 2001

Fat fish b -.044 -.045 SE .008 .008

F -5.718, -5.914

p < .001) < .001

Lean fish b -.062 -.047 SE .010 .009

t -6.012 -5.198

p < .001 <.001

Processed fish

b .023 .029

SE .008 .011

t 3.095 2.731

p < .01 <.001

0,0

1,0

2,0

3,0

4,0

5,0

6,0

1950 1955 1960 1965


Period = 2001

Birth cohort

Period = 1996



Results: Period effects 1996 2001

Fat fish Meals/month 2.06 2.25

SE 0.035 0.035

Lean fish Meals/month 4.05 3.39

SE 0.041 0.047

Processed fish Meals/month 3.2 4.6

SE 0.034 0.048

Sum fish consumption Meals/month 9.28 10.25

SE 0.075 0.087

Pct

+9,2

-16,3

+47%

+10,5



Results: Cohort vs. Biological Age

F i g u r e 2 . L i n e a r e f f e c t s o f b i o l o g i c a l a g e o n c o n s u m p t i o n o f f a t , l e a n a n d p r o c e s s e d f i s h w i t h i n c o n s u m p t i o n p e r i o d s 1 9 9 6 a n d

2 0 0 1 .

0.0

1.0

2.0

3.0

4.0

5.0

6.0

35 40 45


Period = 2001

Biological age

Period = 1996

0.0

1.0

2.0

3.0

4.0

5.0

6.0

35 40 45


Period = 2001

Period = 1996

0.0

1.0

2.0

3.0

4.0

5.0

6.0

35 40 45


Period = 2001

Period = 1996

0.0

1.0

2.0

3.0

4.0

5.0

6.0

1950 1955 1960 1965


Period = 2001

Period = 1996

0.0

1.0

2.0

3.0

4.0

5.0

6.0

1950 1955 1960 1965


Period = 2001

Period = 1996

0.0

1.0

2.0

3.0

4.0

5.0

6.0

1950 1955 1960 1965


Period = 2001

Birth cohort

Period = 1996

F i g u r e 1 . L i n e a r e f f e c t s o f b i r t h c o h o r t o n c o n s u m p t i o n o f f a t , l e a n a n d p r o c e s s e d f i s h w i t h i n c o n s u m p t i o n p e r i o d s 1 9 9 6 a n d

2 0 0 1 .

CohortBiological age

0,0

1,0

2,0

3,0

4,0

5,0

6,0

35 40 45


Period = 2001

Biological age

Period = 1996



Discussion and Conclusion

Processed fish consumption is rising in Norway.

Consumption levels were found to be higher in later birth cohorts, among younger people in general, and in later consumption periods.

The conclusion remains invariant under all different interpretations of the age-period-cohort problem.



Discussion and Conclusion

• Lean fish consumption is falling in Norway• Consumption levels were found to be lower

– in later birth cohorts– among younger women in general– in later consumption periods

• The conclusion remains invariant under all different interpretations of the age-period-cohort problem



Discussion fat fish consumption• Remains ambiguous

– Fat fish consumption has increased totally and for each birth cohort, but not by age

– The households in the cohort have also changed

Birth Cohort Mean 1996

Mean 2001 % Change

1951-1955 3,64 3,12 -14,16 % 1956-1960 3,82 3,67 -4,01 % 1961-1965 3,42 3,83 12,10 %

Age 41-45 3,64 3,67 0,84 % 36-40 3,82 3,83 0,23 %



Discussion fat fish consumption

• Two hypotheses:– (a) an increase over time periods is partially

cancelled by a decreasing household size over birth cohorts, leaving a biological age effect as a mere residual

– (b) The positive relationship with biological age is the true and only underlying effect neutralizing the effect of changing household size and composition



Conclusion

• Fish (Fat) fish consumption changes with age and changing size and composition of households

• Cohort and age predicts – less lean fish consumption– Increased processed fish consumption

• Age predicts – Fat fish consumption

• Cohort predicts consumption for fish products in market segments related to households cycles

age, period, or birth cohort: what determines demographic differences in seafood consumption?...

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