Age, Period, or Birth Cohort: What Determines Demographic Differences in Seafood Consumption? Joachim Scholderer MAPP, The Aarhus School of Business, Denmark Eiliv Lund Institute of Community Medicine, University of Tromsø, Norway Torbjørn Trondsen Norwegian College of Fishery Science, University of Tromsø, Breivika, Norway

IIFET 2002, 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?

IIFET 2002, T. Trondsen. Age, cohort and period.3 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

IIFET 2002, T. Trondsen. Age, cohort and period.4 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

IIFET 2002, T. Trondsen. Age, cohort and period.5 Observed means seafood dinners per month Fat fishLean fishProcessed fish Birth year % change % change % change

IIFET 2002, T. Trondsen. Age, cohort and period.6 Methods Panel data from the Norwegian Women and Seafood Consumption Study (NOWAC) Cohorts selected women born 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

IIFET 2002, T. Trondsen. Age, cohort and period.7 Results: Cohort effects Fat fishb SE.008 F-5.718, p <.001)<.001 Lean fishb SE t p<.001 Processed fish b SE t p<.01<.001

IIFET 2002, T. Trondsen. Age, cohort and period.11 Results: Period effects Fat fishMeals/month SE0.035 Lean fishMeals/month SE Processed fishMeals/month SE Sum fish consumptionMeals/month SE Pct +9,2 -16,3 +47% +10,5

IIFET 2002, T. Trondsen. Age, cohort and period.12 Results: Cohort vs. Biological Age Cohort Biological age

IIFET 2002, T. Trondsen. Age, cohort and period.16 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.

IIFET 2002, T. Trondsen. Age, cohort and period.17 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

IIFET 2002, T. Trondsen. Age, cohort and period.18 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

IIFET 2002, T. Trondsen. Age, cohort and period.19 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

IIFET 2002, T. Trondsen. Age, cohort and period.20 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