The collection of data
What's covered
Key facts
Cleaning data and dealing with problems
A wrongly recorded value can be identified by considering row or column totals, or whether a value is consistent with the other values.
Experiments, reliability and validity
Extraneous variables should be identified and controlled, for example by doing every trial at the same time of day.
Hypotheses and planning an investigation
Confidentiality is a constraint because people may not be willing to reveal confidential information, such as their salary.
Populations, sampling frames and censuses
A census is time consuming and expensive, and is unsuitable when testing destroys or uses up the items.
Primary and secondary data sources
Sources of secondary data should be acknowledged.
Questionnaires, interviews and bias
Processing time for closed responses is much less than for open responses, so they are quicker and easier to count and analyse.
Sampling methods
Cluster sampling groups the population into convenient, usually naturally occurring clusters and samples whole clusters, for example everyone on one production line.
Stratified sampling
Stratified sampling divides (stratifies) the population into groups and then selects a sample independently from each group.
Types of data
Bivariate data is collected as pairs of values, e.g. height and distance jumped for each student.
Cleaning data and dealing with problems
Data may need to be cleaned before further processing, including issues that arise on spreadsheets.
Practice questions with answers
A taste of the 92 questions in this topic, answers marked. Sign up to practise the full set with spaced repetition.
Why may collected data need cleaning before it is processed?
- ✓To find and fix errors so calculations are correct
- •To make the sample size much bigger
- •To remove every value that looks unusual
- •To turn quantitative data into qualitative data
Researchers compare pupils' test scores before and after a flood closed their school. What type of study is this?
- •Controlled experiment
- •Field experiment
- •Laboratory experiment
- ✓Natural experiment
Which of these is a suitable hypothesis?
- •Car maintenance costs are interesting
- •Do older cars cost more to maintain?
- •How much does a car cost to maintain?
- ✓Older cars cost more to maintain than newer cars
What is a sampling frame?
- •A diagram showing how data was collected
- ✓A list of the members of the population
- •The members actually chosen for a sample
- •The time period for collecting data
A student downloads crime figures from a police website. What type of data is this?
- •Bivariate
- •Primary
- •Qualitative
- ✓Secondary
Which of these survey questions is a leading question?
- ✓Don't you agree that school lunches cost too much?
- •How many school lunches did you buy last week?
- •How much do you usually spend on lunch each day?
- •Which lunch option do you choose most often?
Three minutes a day. Knowledge that sticks.
Practise all 92 The collection of data questions with spaced repetition, so what you revise today is still there in the exam. Free to use, no card needed.