The benefits of a longitudinal approach to policy-making Introduction to Understanding Society, 29 th June 2016, Cardiff University Professor Melanie Jones

Cross Sectional Data - “Snapshot” Representative picture at a point in time Comparison across groups Control observable influences No information before or after which limits causal inferences

Disability Related Employment Gap Source: Labour Force Survey 2015

Repeated Cross Sectional Data “Change over time” Another representative picture at a different point in time Sampling frame is the same but actual sample is different Aggregate trends or change over time Achievement relative to policy goals/targets

Disability Related Employment Gap Source: Baumberg et al. (2015)

Longitudinal Data Follow same sample over time –Panel Longitudinal Study (linked Census data) Longitudinal Labour Force Survey British Household Panel Survey –Cohort (birth year) 1958 National Child Development Study 1970 Birth Cohort Study Millennium Cohort Study

What are the benefits of longitudinal data? Individual level change or dynamics –Labour market transitions –Residential mobility Persistence of individual outcomes –Poverty or low pay Particularly important in identifying complete picture (what happens before and after) –Life events (marriage; child birth; ill-health) –Recovery or scarring? –The influence of past events e.g. importance of early years

Difference between expectation and actual Age versus cohort Causality –Timing of events –Control for ‘fixed’ unobservable influences Policy evaluation – before and after comparisons –Treatment and matched control groups What are the benefits of longitudinal data?

Why does disability reduce the probability of employment? Jenkins and Rigg (2004) Selection effect? Onset effect? Duration effect?

Selection DisabledNon-disabled Irregular Continuously Disabled Consistent Onset Consistent Exit Continuously Non-disabled Employment Outcomes Employment Hours Hours (employed) Hourly Earnings (£) Notes: See notes to Table 1. With the exception of hours of work and hourly earnings (which refer to an average) all figures refer to the percentage within the relevant group. Employment characteristics are measured in the first wave. Source: Jones et al. (2013)

Disability Onset Source: Jones et al. (2013)

Onset and Duration Source: Jones et al. (2015)

Onset and Duration Source: Jones et al. (2015)

But longitudinal data also has limitations…. Attrition –People drop out of the survey over time Discrete time points (Census) Often smaller sample than cross sectional data More complex to analyse…..and interpret

References Baumberg, B., Jones, M. and Wass, V. (2015) “Disability Prevalence and Disability-related Employment Gaps in the UK : Different Trends in Different Surveys?”, Social Science and Medicine, 141, p Jones, M., Davies, R. and Drinkwater, S. (2013) “The Dynamics of Disability and Work in Britain”, mimeo, Swansea University. Jones, M., Mavromaras, K., Sloane, P. and Wei, Z (2015) “The Dynamic effect of Disability on Work and Subjective Well-being in Australia” IZA Discussion Paper No Jenkins S. and Rigg J. (2004). Disability and disadvantage: Selection, onset and duration effects. Journal of Social Policy, 33, p

The benefits of a longitudinal approach to policy-making Introduction to Understanding Society, 29 th June 2016, Cardiff University Professor Melanie Jones