Data Collection | DP IB Maths: AI HL Revision Notes 2021

Methods of Data Collection

How do I choose variables to investigate?

Keep the number of variables you investigate to a minimum
- Too many variables at once can be overwhelming
- It can be time-consuming to process unnecessary data
You should choose variables that are linked to what you are investigating
- If you are investigating the ability of adults to solve puzzles you might use the time it takes them as a variable
- Consider which variables are likely to have an effect on what you are investigating
  - An adult’s reading speed will affect their time to solve a puzzle
  - An adult’s height is unlikely to affect their time to solve a puzzle

What makes a good survey?

A survey is a method of collecting data
Consider whether the survey needs to be in-person

A person might be less likely to answer questions truthfully in person
You can quickly survey more people remotely or electronically

Such as postal surveys, phone surveys, internet surveys

Consider whether the interviewer could unintentionally influence participants’ responses

If a headteacher is asking students whether they enjoy school then they are more likely to say yes as they think that is what the headteacher wants to hear
This will introduce bias

What makes a good questionnaire?

A questionnaire is a list of questions
The questions should be unbiased

Questions should not be leading

For example: “You enjoy school, don’t you?”

If options are given for the participant to choose from then they should cover all possible responses

The questions should not be personal

This means you should not ask for unnecessary personal information

Such as date of birth, address, etc

The questions should not reflect your personal opinions

For example: “Do you enjoy watching the boring news on TV?”

People can find it difficult to rate personal feeling/qualities

For example: “How smart do you think you are?”

Questions can be structured or unstructured

Structured questions usually ask the participants to choose from options, give a rating or rank options

These can be quick to analyse
The answer choices should be consistent where appropriate

Unstructured questions let the participants to express their views in their own words

These tend to be more open-ended questions
These can take longer to analyse but can give more in-depth views

Questions should be precise and unambiguous

They should be phrased in a way in which the participants understand exactly what you mean
For example: “Do you study French or Spanish at school” is not precise

Some people might reply with “Yes” or “No”
Some people might reply with “French” or “Spanish”

Reliability & Validity

What is reliability & validity of a data collection method?

Reliability measures how consistent a process is at measuring a variable

A process is reliable if you would get the same results by repeating the process with the same sample using the same conditions

Validity measures how accurate a process is at measuring a variable

A process is valid if it is accurately measuring the variable you want it to measure

If your process is found not to be reliable or valid then:

Adjust the data collection process
Change the sampling technique
Use a larger sample

What are tests to check reliability?

Test-retest

This is where you use a data collection process with a sample and then repeat the same process with the same sample at a later time

The results should show positive correlation if the process is reliable
The results might not perfectly match due to external factors during the gap between the data collection
Once the sample has been through the process once they will be familiar so this could lead to different results from the second process

Parallel forms

This is where you give the same sample a second set of questions (or second set of experiments) which are similar to the first set

The results should show positive correlation if the process is reliable
It can be difficult to make the two processes similar to each other

What are tests to check validity?

Content-related validity checks

This is where you check how well the process measures all aspects of the variable

If the process is valid then it should cover all aspects of the variable
These checks require knowledge of the variable so experts are often used
An example of a process that is valid:
A teacher wants to assess how well students understand calculus so they set questions covering differentiation, integration and applications
An example of a process that is not valid:
A restaurant manager wants to assess how good a chef is at cooking steaks so asks the chef to make 10 medium steaks

Criterion-related validity checks

This is where you check how well one variable predicts the outcome for another variable (called the criterion variable)

If the process is valid then the variable should be a good predictor
An example of a process that is valid:
Results from a mock exam being used to predict the results in the actual exam
An example of a process that is not valid:
Results from measuring the heights of meerkats being used to predict the heights of squirrels

Worked example

Tomas is a dog trainer. Before he agrees to train a dog he assesses the dog’s obedience. To do this, he first visits the dog, asks it to perform 10 basic commands and records how many the dog successfully carries out. Two days later, Tomas visits the dog a second time and asks it to do the same 10 commands. Tomas assesses 8 dogs using this process and the table below shows the number of commands performed successfully by each dog on each visit.

Dog	1	2	3	4	5	6	7	8
First visit	3	5	2	3	6	2	0	5
Second visit	3	5	2	4	5	2	1	5

State the reliability test that Tomas is using.

4-1-2-ib-ai-hl-reliability--validity-a-we-solution

Comment on the reliability of Tomas' process.

4-1-2-ib-ai-hl-reliability--validity-b-we-solution

Data Collection (DP IB Maths: AI HL)

Revision Note