A ‘census’ happens when we ask all the people in the land to answer some questions and then add up all the answers. One of the things that I do at work is help people to use the numbers that we find when we add everything up. In this land (‘United_Kingdom’), we ask these questions every ten years. We have been doing this for more than two hundred years.
We can use the answers to find out how many people there are: how many men, how many women, how many children and so on. The questions cover things like the jobs that people do, the houses that they live in, and the people that they live with. So, we can find out how many people do different sorts of jobs, and what different sorts of people do the same job. We also ask questions about how well people did at school, about whether they look after other people and about whether they are sick or well.
When we check the answers, we can do things like looking at the number of different sorts of people who do a job. Sometimes there are less women in some jobs than we would expect, sometimes less people who believe in different Gods, and sometimes less people with different colored skin. If we find things like this we worry that different people are not all being given the same chances.
When I said that there might be less people who believe in different Gods doing a job than we would expect, how do we know how many we should expect? We can find out by looking at how many people there are in each group in all the people, and then seeing if there is the same share in the people doing each job. If we did not ask all the people, we might just have to guess about this.
A question that I am interested in asks people about where they used to live a year ago. This lets us see how many people have changed the place that they live in, and how they have all moved about. This helps us to decide where we might need to build new schools or hospitals or other things. If lots of people with children have moved to a place, then we might need to build a new school there.
One of the most interesting things that we can do is find the answers that a person made the last time that they answered the questions, and the answers that the same person gave ten years before. We can also look at their answers from ten years before that, and ten years before that, and even ten years before that! We will only find all of their answers if they are old enough, of course. If they are younger, or if they came to this land not many years ago, we will only find some of their answers. When we look at all these answers from different times, we can start to understand how things that people did a long time ago - such as the job that they did, or how well they did at school, or what their family was like or the jobs that their parents did - might change the way that their life turned out as they got older.
We can join the answers from now and from ten years ago (and earlier) for a small group of people. You and I do not know if we are in this group. The joined up answers give a huge number of facts about a person - so many that it might be easy to work out who that person is, even though we are not told their name or where they live. That is why it is important that people do not know if they are in this small group, and also why the actual numbers have to be kept under lock and key! People who use the numbers for this small group are told what they can and can not tell other people: they must make a serious promise not to tell things that might let others work out the name of someone in the small group.
After one hundred years have gone past, all the answers that people gave can be shown to everyone. People can find out very interesting things that happened to their family long before anyone who is living now can remember.
Some of the people who run this land have said that they don’t think that we should have carry on asking these questions to all the people. One reason for this is that it takes a lot of money to ask all the people lots of questions - paper forms have to be sent to all the houses, and other people have to read all the completed forms, and type the answers into a computer. It is true that it takes a lot of money, but it is important to remember that although we ask the questions every ten years, we keep on using the answers for a long time after. A lot of the ways that we use the answers are to try to make sure that we save money at other times: such as not building a new school when there are not enough children to go to it.
If we did not ask questions of all the people, what could we do instead? In some lands, they do not ask these questions. However in those lands they usually have a computer that keeps track of people, so that they always know how many different sorts of people there are in each place. In this land, we do not have a computer like that, so we can not use it in the same way. Sometimes, we ask questions to a group of people, instead of all the people. If that group has the same share of different sorts of people that we can see in all the people, then we think that the answers would be the same for all the people. It saves a lot of money to only ask questions to a group of people. But there is a problem with this! How do we know that the group of people has the same share of different sorts of people as there are in all the people? This is part of the same problem that I mentioned above, when we worry about whether people have the same chances. We need to ask questions to all the people from time to time to make sure that we still know how many different sorts of people there are!”