What is Natsal?

To get data that represent the British population, people are selected at random to take part in the survey from a list of all addresses in Britain. A highly-trained interviewer asks the participant questions and enters their responses in a laptop. Sometimes the interviewer uses ‘showcards’ which represent a range of possible responses – often where answers might be perceived as being a little bit personal - so that the participant just needs to report a letter code rather than say aloud something that might embarrass them. For example, the questions on attitudes, which ask the participant for their opinions about different types of sexual relationship.

For the most sensitive questions, the interviewer hands over the laptop and the participant reads the questions on the screen and enters their responses themselves. This ‘self-completion’ approach is used so their response remains entirely confidential. In fact, for this part of the interview, the computer programme is designed to lock so that when the participant returns the laptop to the interviewer they can’t then see the participant’s responses.

The Natsal survey ends with some final face-to-face questions so that the interview doesn’t end on a particularly sensitive note. As questions in Natsal are deeply personal and for some unsettling or upsetting, all participants are given a list of helplines and websites of organisations that help people with some of the topics addressed in the survey.

Over 450 interviewers of all ages, genders and walks of life went through extensive training to carry out the interviews for Natsal-3. Many interviewers have previously completed training for earlier Natsal surveys – including a few who have done so for all Natsal surveys to date.

The interviewer’s role in Natsal is crucial for its success in several ways. Firstly, from the randomly-selected household the interviewer selects one person – at random – to participate in the survey. This is important as it helps to make the findings broadly representative of the general population.

Research has shown that if a household is asked to select a person themselves then it is quite often the person who most wants to talk about sex that does so. This ‘self-selection’ jeopardises representativeness.

Secondly, the interviewer is trained to encourage people to take part, tailoring reasons for participating to the potential participant to demonstrate the relevance of Natsal to them and emphasising the importance of their participation.

Thirdly, the interviewer builds rapport with the participant by asking them the first set of questions so that when they answer the more sensitive questions in the CASI, halfway through the interview, they feel more confident about the process and the importance of answering questions as honestly and accurately as they can.

Almost – yes. So whether someone lives in the remote countryside or in the heart of a city, Natsal is designed so that nearly everyone in Britain has the same chance of taking part regardless of where they live.

However, for practical reasons, addresses in the Scottish Highlands (north of the Caledonian Canal) and the Scottish Islands and the Isles of Scilly are excluded. This means that 0.5% of eligible addresses in Britain are therefore excluded. 

Another important point to note is that the ‘sampling frame’ (that is, the register used to randomly select people to invite to take part in Natsal-3) was the Postcode Address File which consists of all private residential addresses in Britain. This means that people who are homeless or living in an institution like a prison or in residential care are excluded.

On the whole, participants answer all the questions that are asked. Occasionally a participant will choose not to answer a particular question, but for most questions less than 3% of those eligible to answer will refuse to do so.

Despite Natsal asking some very sensitive questions about sexual behaviour and sexual health, the question that has the highest ‘item non-response’ in Natsal is the one about household income.

While some participants may refuse to answer this question as they consider it too intrusive, others may simply not know the answer as the question is about household income – especially those living in shared accommodation or younger participants living with their parents.

In line with other health surveys undertaken around the same time, for Natsal-3 a similar proportion of people - around six in ten - said ‘yes’ when asked to take part in Natsal (this is called the ‘response rate’).

The response rate may be lower for the next Natsal survey as declining response rates are an ongoing challenge facing survey-based research in general.

However, statisticians have shown that lower response rates do not necessarily mean lower quality data. Nevertheless, steps are taken to ensure the resulting data are as representative as possible of the population as a whole, including making sure that under-represented groups are included in sufficient numbers where possible.