About our analysis
Information about our measurement framework for social mobility – the Social Mobility Index – and an introduction to the main statistical concepts used in State of the Nation 2023. For more information, see the main technical annex on GOV.UK.
Monitoring social mobility: the Social Mobility Index
The Social Mobility Commission (SMC) monitors social mobility across the UK. We aim to understand how many people are socially mobile, in what parts of the country, and whether a person’s background can limit their opportunity.
Monitoring social mobility is complex and difficult. Data can be hard to get hold of or may not exist at all, such as income records linked across generations. Where data does exist, it can be very hard to interpret. This is why we created the new Social Mobility Index (the Index), first published in 2022. We took the best available advice from academics, policymakers, and charities working in social mobility.
Social mobility outcomes and drivers
Our index presents a framework for monitoring social mobility in the UK. It consists of 3 types of measures: mobility outcomes, intermediate outcomes and drivers. Looking at all of these measures can inform us how social mobility has changed in the past and how it might develop in the future.
Mobility outcomes are about making progress from your parents’ position to your own eventual position as an adult. For example, we might compare people’s incomes at around the age of 50 years. We look at:
- occupational class
Intermediate outcomes are similar, but we look at people’s progress from their parents’ position to their own position at an earlier point in life, such as employment in their 20s or educational attainment at age 16 years. This is important, because a person’s outcomes in their 20s can be a very good indicator of how their later life will turn out. It also means that we don’t have to wait 30 or 40 years for one’s full mobility outcomes before we have an indication of how their social mobility prospects fare.
Mobility and intermediate outcomes both break outcome measures down by people’s socio-economic background (SEB). This can show how different starting points might affect later progress.
Drivers of social mobility
Drivers are the background conditions that make social mobility easier or more challenging. We have included things as drivers if we think they may affect overall social mobility rates. For example, the availability of good schools is a driver, because it helps people who would not otherwise have had an opportunity to be upwardly mobile. Drivers tell us about these nationwide and regional background conditions.
However, drivers do not tell us what the UK’s rates of mobility currently are, and they are not broken down by SEB. The question of what is or is not a driver is also distinct from the question of what might help someone achieve upward mobility (for example, getting a good degree).
This year, we have developed composite indices for some of our drivers and intermediate outcomes. These are measures that add and summarise multiple measures into one overall score.
This is useful because the estimates for individual areas often involve sampling errors due to being based on sample surveys, and therefore need to be treated with caution. The sample surveys, such as the Labour Force Survey, contain relatively small samples within each area. Sample sizes become even smaller when we focus on results for specific age or ethnic groups, as with the intermediate outcomes.
The imprecision of the survey-based statistics means that we cannot confidently draw conclusions about the differences in outcomes between geographical areas. Indeed, very few areas prove to be significantly different from the national average when single indicators are used, such as unemployment or earnings.
The new composite indices give a summary of how different geographical areas of the UK compare on the main dimensions of mobility identified from the data. This is useful because there’s always a risk that differences between areas in respect of a single measure could be due to random sampling errors. But when multiple measures all give a similar picture, we can be more confident that there are real differences among the areas.
How the data was produced
There are many data sources used to produce our index. Some of these, such as the Labour Force Survey, involve analysing raw individual level data before our indicators can be created.
Other sources, such as the educational attainment statistics from the Department of Education, have already been analysed, with the statistics readily available in the public domain.
See our technical annex for more details of our main data sources and the methodology of each of our indicators.
We define people’s socio-economic background according to the occupation of their highest-earning parent. Our occupational classes are based on the National Statistics Socio-Economic Classification (NS-SEC) which is the official socio-economic classification of the UK, as set by the Office for National Statistics (ONS).
To simplify our analysis, we have collapsed the 8 classes provided by the ONS into the following 5 categories:
- higher professional (NS-SEC group 1) – examples include CEOs, doctors and engineers
- lower professional (NS-SEC group 2) – examples include teachers, nurses and journalists
- intermediate (NS-SEC groups 3 and 4) – examples include shopkeepers, taxi drivers and roofers
- skilled working class (NS-SEC groups 5 and 6) – examples include mechanics, electricians and housekeepers
- routine working class (NS-SEC groups 7 and 8) – examples include cleaners, porters and waiters
For a more detailed picture of how certain groups of the population are experiencing social mobility, we split our mobility outcomes and intermediate outcomes by some protected characteristics (sex, ethnicity and disability status) and geography where possible.
We use quintiles in all maps. A quintile represents a fifth (20%) of the population. This is calculated by ordering the regions from lowest to highest values (usually percentages) and then dividing them into 5 groups of equal size – such as from 1 (lowest) to 5 (highest). Each group is called a quintile.
The data shown in our maps is purely descriptive and we are not yet in a position to claim any causal effects of regions on outcomes. Because these statistics are based on sample surveys, they are affected by sampling error.
As the values we present are estimates in most cases, this means there is a degree of uncertainty over how likely they are to reflect the true value in the population. We use confidence intervals to represent this degree of uncertainty.
According to the ONS: "A confidence interval gives an indication of the degree of uncertainty of an estimate and helps to decide how precise a sample estimate is. It specifies a range of values likely to contain the unknown population value. These values are defined by lower and upper limits. The width of the interval depends on the precision of the estimate and the confidence level used. A greater standard error will result in a wider interval; the wider the interval, the less precise the estimate is."
We use 95% confidence intervals in our analysis. According to the ONS: "This means that if we drew 20 random samples and calculated a 95% confidence interval for each sample using the data in that sample, we would expect that, on average, 19 out of the 20 (95%) resulting confidence intervals would contain the true population value and 1 in 20 (5%) would not. If we increased the confidence level to 99%, wider intervals would be obtained."
Read more about confidence intervals and dealing with uncertainty on the ONS website.
We follow a general rule of rounding upwards to the nearest whole number. In some cases, we provide 1 or 2 decimal points when the numbers are small, when the decimal point might make a difference to the interpretation, or when we are presenting financial data, such as hourly earnings.