Dr Roland SimonsStrategic Policy and Education Futures

13 September 2005

What are some key strengths and issues for them?

What are longitudinal surveys?

What is a Longitudinal Survey?What is a Longitudinal Survey?

Working Definition – Longitudinal StudyWorking Definition – Longitudinal Study

“A study of a group of subjects “A study of a group of subjects that follows them through time.”that follows them through time.”

Obviously, the essential building block of the longitudinal survey is a single ‘point in time’ survey itself….

Therefore, the issues and strengths of a single survey will also apply to longitudinal surveys.

Note: The aim of these slides is to (1) describe longitudinal surveysand (2) to outline some of the strengths and issues associated with them.

What is a Longitudinal Survey?What is a Longitudinal Survey?

Single Survey – Single CohortSingle Survey – Single Cohort

Strengths• Standardised questions• Able to collect data from large #sIssues• Obtaining representative sample• Ensuring clear/reliable measures

But this does not tell us about actual trend and only tells us about one group. So let us move to a more complicated survey.

For example if we wanted to assess the pathways and destination of students we could run a “one-off” survey of 14 years olds and ask them about their future aspirations and past experiences. But this assumes that they will have a good memory and be able to predict their future.

14 year olds

September 2005

Cohort A

What is a Longitudinal Survey?What is a Longitudinal Survey?

Single Survey – Multiple CohortsSingle Survey – Multiple Cohorts

Strengths• Standardised questions• Able to collect data from large #s• Ability to infer trend from cohortsIssues• Obtaining representative sample• Ensuring clear/reliable measures• Assuming cohort comparability

14 year olds

September 2005

Cohort A

16 year olds

September 2005

Cohort B

By comparing results of 14 year olds to 16 year olds at a single ‘point in time’ we might infer changes over time but we would have to assume the cohorts aresimilar in their experience, backgrounds, etc.,

But this still does not tell us about cohort specific trends over time. What if the two cohorts are different? Inferring a trend in such cases would be problematic. So let us move to a more complicated survey.

What is a Longitudinal Survey?What is a Longitudinal Survey?

Longitudinal Survey – Single CohortLongitudinal Survey – Single Cohort

14 year olds

September 2005

Strengths• Standardised questions• Larger volumes of data• Longitudinal comparisons• Statistically powerful dataIssues• Obtaining representative sample• Maintaining sample size• Clear/reliable measures• Question Relevance/time• Cost• Organisational complexity

16 year olds

September 2007

18 year olds

September 2009

Cohort A

This approach does not allow for the study of experiences for different cohort groups. So let us move to a more complicated survey.

So now we are tracking students from a single cohort over time and this allows us to identify relationships and, perhaps, causal linkages over time.

What is a Longitudinal Survey?What is a Longitudinal Survey?

Longitudinal Survey – Multiple CohortsLongitudinal Survey – Multiple Cohorts

14 year olds

September 2007

16 year olds

September 2009

Cohort B

Strengths• Standardised questions• Larger volumes of data• Longitudinal comparisons• Multiple cohorts• Ability to compare cohorts• Statistically powerful dataIssues• Obtaining representative sample• Maintaining sample size• Clear/reliable measures• Question Relevance/time• Cost• Organisational complexity• Assuming cohort comparability

With more cohorts the ability to describe differential experiences for samples increases. However, so does the complexity of the research. Projects such as LSAY are very complex and expensive and require extensive planning.

14 year olds

September 2005

16 year olds

September 2007

18 year olds

September 2009

Cohort A

What is a Longitudinal Survey?What is a Longitudinal Survey?

Therefore Longitudinal Surveys are:Therefore Longitudinal Surveys are:

Often considered the ultimate in surveying practice Highly complex and difficult to organise / analyse Are expensive to run Require considerable pre-planning and attention to detail to

– Minimise attrition over time– Maximise sample representativeness– Maximise item clarity (or validity and reliability) over time– Ensure enough funding and commitment is made over the long-term– Balance stakeholder interests and benefits from the research– Ensure meaningful interpretation of the findings– Balance the long-term research value with the immediate needs of

stakeholders