Handling Data · Data · Lesson 1
Choosing and Justifying a Method of Collecting Data
Before a market queen buys stock, a coach picks a team or a Minister announces a plan, someone must first gather facts. In this lesson you will learn the main kinds of data, the seven common ways of collecting it, and how to choose the best method for a question and explain why.
By the end you will be able to
- ✔Distinguish quantitative (numbers) from qualitative (descriptions) data.
- ✔Name and describe questionnaires, interviews, observation, experiments, surveys, databases and the internet as methods of collecting data.
- ✔Select the most suitable method for a given question and justify the choice.
- ✔Explain why a sample must be fair and give an example of a biased sample.
Key words
- Data
- Facts, figures or information collected to answer a question.
- Quantitative data
- Data that are numbers or measurements, such as the number of desks or the price of a plate of waakye.
- Qualitative data
- Data that describe qualities or opinions in words, such as favourite colour or the make of football boots.
- Survey
- Collecting information from a group of people, usually by questionnaire or interview.
- Sample
- A smaller group chosen from a larger group (the population) to represent it.
Curriculum reference
Content standard: B7.4.1.1 Select, justify, and use appropriate methods to collect data (quantitative and qualitative), display and analyse the data (grouped/ungrouped) presented in frequency tables, line graphs, pie graphs, bar graphs or pictographs and use these to solve and/or pose problems.
Indicator: Select and justify a method to collect data (quantitative and qualitative) to answer a given question.
Starter
Which drinks should we buy?
Your class is planning an end-of-term party for 45 learners. Kofi says everyone loves Fanta, Ama says most people prefer Sobolo, and Yaw wants Malta. If you just buy what the loudest person wants, half the class may go thirsty! The only fair way to decide is to collect facts, and the way you collect them matters just as much as the facts themselves.
1. What is data? Quantitative and qualitative
Data means facts and figures that we gather so that we can answer a question. A trader at Kejetia Market keeps data on how many tubers of yam she sells each day. The Ghana Football Association keeps data on goals scored. The Ghana Meteorological Agency keeps data on rainfall. Without data we can only guess; with good data we can make sound decisions.
Data come in two main kinds. Quantitative data are numbers that you can count or measure. Qualitative data are descriptions, qualities or opinions that are usually written in words.
| Type | What it tells us | Ghanaian examples |
|---|---|---|
| Quantitative (counted) | How many | Number of desks in a classroom; number of goals scored by the Black Stars |
| Quantitative (measured) | How much, how long, how heavy | Daily bus fare in cedis; height of learners; mass of cocoa in a bag |
| Qualitative | What kind, which one, what opinion | Favourite subject; make of football boots; mobile network used |
▶ Notice that quantitative data answer 'how many or how much', while qualitative data answer 'which kind or what opinion'.
2. Seven ways of collecting data
There is no single best way to collect data. Each method has strengths and weaknesses. The NaCCA curriculum lists these methods:
| Method | How it works | Good for | Weakness |
|---|---|---|---|
| Questionnaire | A printed or online list of written questions that people fill in | Many people, personal opinions, cheap | Some people do not return it or answer honestly |
| Interview | You ask questions face to face or by phone and record the answers | Detailed reasons and feelings | Slow; only a few people can be reached |
| Observation | You watch and record what happens, without asking | Counting things or behaviour, e.g. vehicles passing a junction | Cannot tell you why people act that way |
| Experiment | You change one thing under control and measure the result | Testing cause and effect, e.g. two fertilizers on maize | Needs time, equipment and fair conditions |
| Survey | Asking a chosen group the same questions (using questionnaires or interviews) | Finding opinions of a large group | Needs a fair sample |
| Database | Using records that are already stored, such as school registers or Ghana Statistical Service tables | Past figures and large amounts of data | Data may be old or not exactly what you need |
| Electronic media / internet | Searching websites, news and reports | Quick facts, prices, comparisons | Information may be wrong; check the source |
Data you gather yourself, first-hand, are called primary data (a questionnaire to your classmates). Data that someone else already collected and you simply use are called secondary data (a table from a database or a website).
3. Choosing a method and justifying it
To select a method means to pick one. To justify it means to give a reason. A good answer always has the form: 'I would use method because reason linked to the question.'
- 1Read the question and decide what you need to find out: numbers, opinions, or a cause-and-effect link?
- 2Decide who or what has the facts: people, objects, past records or an experiment?
- 3Pick the method that gets those facts most accurately and fairly in the time you have.
- 4Write your justification: 'I will use … because …'.
| Situation | Suitable method | Reason |
|---|---|---|
| Type of drinks to buy for a class party | Survey with a questionnaire | Everyone's opinion is needed and the question is simple to ask all 45 learners |
| Make of football boots for the school team | Interview the players (and check prices on the internet) | Players know what fits well; the internet gives prices |
| Do people who eat more fufu develop a pot belly? | Observation and measurement, supported by a questionnaire | We must measure waist size and ask how often people eat fufu; an experiment would be unfair to people |
| Number of desks in each classroom | Observation (counting) | The desks are there to be counted; asking people may give wrong numbers |
| Bus fare B6 learners pay every month | Questionnaire | Each learner knows their own fare; it is a number |
| Buying a mobile phone from an online shop | Internet / electronic media | Compare prices, specifications and customer reviews |
4. Fair samples and common mistakes
Often we cannot ask everybody. Asking everyone in a group is a census. Asking only some is a sample. A sample is useful only if it is fair: every member of the group must have an equal chance of being chosen. For a school of 600 learners, picking every 10th name on the register gives a fair sample of 60 learners.
A sample that favours some members is biased. If you ask only the players in the Basic 7 football team what the school should spend its sports money on, you will probably hear 'footballs and boots', but the netball and athletics teams would disagree.
Think also about honesty and respect. Tell people why you are collecting the data, ask permission, and never write down a person's name on a form unless it is really needed. Many people answer more truthfully when they know their answers will be kept private. Finally, choose clear words: a question such as 'Do you like school?' can mean many things, while 'How many days did you come late last month?' gives a number that everyone understands in the same way.
Finally, always make sure your question is clear and your method is practical: do you have enough time, money and permission? The best method on paper is no use if you cannot carry it out.
Worked examples
Try each one yourself first, then open the solution and compare every step.
Example 1
Quantitative or qualitative?
Show the solution
- Step 1(a) Goals are counted, so the data are numbers: quantitative.
- Step 2(b) A favourite subject is a name or opinion: qualitative.
- Step 3(c) Mass is measured in kilograms: quantitative.
- Step 4(d) A make such as Samsung is a name: qualitative.
Answer: (a) quantitative, (b) qualitative, (c) quantitative, (d) qualitative
Example 2
Number of desks
Show the solution
- Step 1The desks are objects that can be seen and counted.
- Step 2Observation (counting) is the most accurate way, because people may guess wrongly.
- Step 3Record the count for each classroom in a table.
Answer: Observation, because the desks can be counted directly and counting is more accurate than asking.
Example 3
Pot belly and fufu
Show the solution
- Step 1He needs two kinds of facts: how often people eat fufu (ask) and the size of their waists (measure).
- Step 2Use a questionnaire for how many times a week each person eats fufu.
- Step 3Use observation and measurement with a tape measure for waist size, with permission.
- Step 4Compare the two sets of data. Justify: an experiment forcing people to eat fufu would be unfair, so we observe real habits instead.
Answer: A questionnaire plus observation (measurement) of waist size.
Example 4
A fair sample
Show the solution
- Step 1Sample fraction = 60 out of 600 = 1 out of 10.
- Step 2So choose every 10th name on the register, starting from a random name.
- Step 3Percentage surveyed = 60 ÷ 600 × 100 = 10%.
Answer: Choose every 10th learner on the register; 10% of the school is surveyed.
Example 5
Choosing from three sources
Show the solution
- Step 1(i) Price: internet or visiting shops (observation); it is a fact that already exists.
- Step 2(ii) Feelings: questionnaire or interview; only the learners can tell us their opinions.
- Step 3(iii) Seeds: experiment; plant both in the same soil with the same water and light, then measure the height after two weeks. The fair conditions show which seed is better.
Answer: (i) internet/observation, (ii) questionnaire/interview, (iii) experiment.
Summary
- Data are facts collected to answer a question. Quantitative data are numbers; qualitative data are descriptions or opinions.
- Methods include questionnaires, interviews, observation, experiments, surveys, databases and the internet.
- To justify a method, say 'I will use … because …' and link the reason to the question.
- Primary data are collected by you; secondary data come from existing sources.
- A sample must be fair, not biased, so choose members by a rule such as every 10th name.
Practice: 15 questions
5 easy, 5 medium, 5 hard. Each one is marked straight away, with a full worked solution.
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