Data Collection
Types of Data
Qualitative (Categorical)
Data in categories or labels β cannot be measured on a number scale.
- Eye colour, favourite subject, type of pet
Quantitative (Numerical)
Data that can be measured or counted.
- Discrete: takes specific separate values (usually whole numbers): number of siblings, shoe size
- Continuous: takes any value within a range: height, temperature, time
Primary vs Secondary Data
Primary data: collected by the researcher for this specific purpose (surveys, experiments) Secondary data: already collected by someone else (census data, published statistics)
Sampling Methods
Random sampling: every member has an equal chance of being selected. Most unbiased.
Systematic sampling: select every nth member (e.g., every 10th person on a list)
Stratified sampling: divide population into groups (strata), sample proportionally from each
Convenience sampling: sample whoever is easiest to reach β biased, avoid for serious studies
Good Questionnaire Design
- Questions should be clear and specific
- One idea per question (no double questions)
- Avoid leading questions that suggest a preferred answer
- Response options should be exhaustive and non-overlapping
- Include a time frame if relevant
Census vs Sample
Census: data from the entire population (expensive, but complete) Sample: data from a subset β quicker and cheaper, but may not represent the whole