1. Melissa Davy Office for National Statistics
Pseudo-cohort analysis - trends in smoking data using the General Household Survey
Melissa Davy
Office for National Statistics

2. Introduction Why we carried out pseudo cohort analysis (PCA)
The advantages and disadvantages
The survey we used in our analysis
The methods we used
Work through an example

3. Why is it useful to look at cohort analysis?
Interested in inequalities over time and by birth cohort
People in different birth cohorts have different experiences
Cohort analysis provides a better understanding of how events change over time

4. What is pseudo-cohort analysis?
- panel data
- same individual
Pseudo-cohort analysis
- cross-sectional data
- average experience of a given cohort
For example
- aged 20 to 25 in a 1980 survey
= 21 to 26 in 1981
= 22 to 27 in 1982
= 44 to 49 in 2004.

5. Advantages of pseudo-cohort analysis
Uses data that are already available
New sample each year so no problem of non-random attrition
Less burden on respondents
More frequent data

6. Disadvantages of pseudo-cohort analysis
Variations in the nature of the samples surveyed
Looking at average experience of the cohort limits the use of the data
Recall bias
Not straightforward
Small cell sizes

7. General Household Survey
Dataset goes back more than 30 years
The GHS covers a range of topics
Relatively large sample size
High quality data source

8. Extracting the data
– create a database which includes all survey years
– create a birth cohort variable
Disadvantages
- Time consuming
Advantages
Valuable research tool
Exploiting full potential of the GHS data
Makes time series analysis easier

9. Creating the dataset Long process documented in:
Uren Z (2006) The GHS Pseudo Cohort Dataset (GHSPCD): Introduction and Methodology. Survey Methodology Bulletin, no 59, pp25-37.
Available at:
contains over 40 variables,
records for over 800,000 individuals.

10. The smoking example Analysis of smoking among men trends over time
trends by age
pseudo-cohort analysis
- interaction of time and age

24. Main findings
At every age, men smoke less than the previous generation.
Not due to established smokers giving up more rapidly
In the most recent cohorts
- fewer men were starting to smoke
but were then giving up at a slower rate than in the past.
Smoking prevalence rates may be stabilising.

25. Conclusion
Pseudo-cohort analysis gives us a better understanding of the GHS smoking data