Week 2 - Collecting Data

What is a Census?

A census is an official survey of the population of a country that is carried out in order to find out how many people live there and to obtain details of such things as people's ages and jobs.

In New Zealand, every five years Stats NZ run "the census" – the official count of how many people and dwellings there are in New Zealand. They ask everyone to complete a set of questions about themselves and their household, so they can capture a snapshot of who is living in, and visiting, New Zealand. The census is the only data collection in New Zealand that covers the whole population. It provides the most complete picture of life in our cities, towns, suburbs, and rural areas. The data helps the government plan services. These include hospitals, kōhanga reo, schools, roads, and public transport. Councils, iwi, businesses, and other organisations also use the data to work out the needs in their area. 

Village of 100 People

The following video looks at what it would look like if we took the entire population of New Zealand, and made it a village of only 100 people (like a percentage). This video was made from the census data collected in the 2013 New Zealand Census. 

And for comparison, the video after that is the same idea, but about Australia, using data from the 2016 Australian Census.

What is a Sample?

In statistics, we don't often collect data about an entire population, as this can be quite hard to do! Usually we collect data by surveying or looking at a subgroup of a population - this is called a sample. We can then use the data we collect to make predictions about the entire population.

For example, if I wanted to know the top 5 favourite foods of Year 9 students, it might be quite hard to ask everyone. However, I could just ask one form class and use my results from that survey to make predictions for the top 5 favourite foods in all of Year 9. 

You should think about why sample data might not always be good at helping us make predictions about a population, especially if our sample isn't chosen random. Some of this will be explained in the video about planning to collect data below. 

Planning to Collect Data Through an Experiment

Sometimes we want to collect data about certain aspects of people's life they may not be able to answer of the top of their head. For example, a person's height. In order to collect the data we may need to conduct an experiment, that is, in this case measure people's height. When running an experiment, it's really important that everyone participating goes about it in the exact same way so that the data collected is accurate.

If we think about our taking a person's height example, these are some things to consider:

• Should the person wear shoes or not?

• What unit of measurement do we use to measure their height?

• What do degree of accuracy to we require - is it to the nearest cm? Or nearest mm?

• Do they lean against a wall or stand freely?

• Do you take it to the top of their head, or the top of their hair?

These are just a few things to consider, and there's probably more! The key message here is that when you are planning to collect data using an experiment, then you must set out a plan that can be easily followed by everyone that removes all the variability, to ensure we gather accurate data.