### Collecting and classing data

Data is of facts, numbers and other information. Statistics involves process of collecting data and using it to try and answer the question. The flow diagram shows four main steps involved in this process of statistical investigation.

### Different types of data

How many brothers and sisters do you have?

You answer to the first question will be the name of a person. Your answer to the second question will be a number. Both the name and the number are types of data.

Categorical data is non-numerical data. It names or describes something without reference to number size. Colors, names of people and places, yes and no answers, opinions and choices are all categorical. Categorical data is also called qualitative data.

Numerical data is data in number form. It can be an amount, a measurement, a time or a score. Numerical data is also called quantitative data (from the word quantity).

Numerical data can be further divided into two groups:

discrete data– this is data that can only take certain values, for example, the number of children in a class, goals scored in a match or red cars passing a point.When you count things, you are collecting discrete data.

continuous data– this is data that could take any value between two given values, for example, the height of a person who is between 1.5 m and 1.6m tall could be 1.5m, 1.57m, 1.5793m, 1.5793421m or any other value between 1.5m and 1.6m depending on the degree of accuracy used. Heights, masses, distances and temperatures are all examples of continuous data. Continuous data is normally collected by measuring.

Tip! One way to decide if data is continuous is to ask whether it is possible for values to be fractions or decimals. If the answer is yes the data is usually continuous .But be careful:

• Age may seem to be discrete because it is often given in full years, but it is actually continuous data because we are getting older all the time.
• Shoe size are discrete even though you can get shoes in half sizes, because you cannot get shoes in size $\displaystyle 7\frac{1}{4}$ or $\displaystyle 7\frac{3}{4}$.

### Methods of collecting data

Data can be collected from primary sources by doing surveys or interviews, by asking people to complete questionnaires, by doing experiments or by counting and measuring. Data from primary sources is known as primary data.

Data can also be collected from secondary sources. This evolves using existing data to find the information you need. For example, if you use data from an internet site or even from this site to help answer a question, to you this is secondary source. Data from secondary sources is known as secondary data.

### Organizing data

When you collect a large amount of data you need to organise it in some way so that it becomes easy to read and use. Tables (tally tables, frequency tables and two-way tables) are the most commonly used methods of organizing data.

### Tally tables

Tallies are little marks $\displaystyle \left( {////} \right)$that you use to keep a record of items you count. Each time you count five items you draw a line cross the previous four tallies to make a group of five $\displaystyle \left( {\cancel{{////}}} \right)$. Grouping tallies in five makes it much easier to count and get a total when you need one.

A tally is used to keep a record when you are counting things.

An example of a tally table:

A student used this to record how many cars of each color there where in the parking lot. He made a tally mark in the second column each time he counted a car of a particular color.

Example 1: John wanted to find out what people thought about pop-up adverts on their social media feeds. She did a survey of 100 people. Each person chose an answer A, B, C or D.

Advertising should be strictly controlled on social media. Pop-up adverts should be banned from all social media feeds.

I strongly agree

I agree

I disagree

I strongly disagree

She recorded these results:

a) Draw a tally table to organize the results.

Count each letter. Make a tally each time you count one.

It may help to cross the letters off the list as you count them. Check that your tallies add up to 100 to make sure you have included all the scores. (You could work across the rows or down the columns, putting a tally into the correct row in your table, rather than just counting one latter at a time).

b) What do the results of her survey suggest people think about pop-up advertising on social media?

The results suggest that people generally don’t think advertising should be banned on social media, 57 people disagreed or strongly disagreed. Only 24 of the 100 people strongly agreed with John’s statement.