Mutually Exclusive Options: Response intervals must not overlap. If options are '1-3' and '3-5', a respondent with the value '3' would not know which box to tick, leading to data errors.
Exhaustive Categories: The set of options must cover every possible answer. This is often achieved by including an 'Other' category or ensuring the ranges cover the full spectrum from zero to a maximum limit (e.g., '0', '1-2', '3-5', 'More than 5').
Grouped Data: For continuous variables like age or time, data is often grouped into class intervals. This makes the questionnaire easier to complete and the resulting data easier to summarize in frequency tables.
The choice between open and closed questions depends on the research goals and the stage of the investigation.
| Feature | Open Questions | Closed Questions |
|---|---|---|
| Response Type | Free text / Descriptive | Tick boxes / Multiple choice |
| Data Type | Qualitative | Quantitative |
| Analysis | Time-consuming, subjective | Fast, objective, statistical |
| Flexibility | High - captures unexpected ideas | Low - limited to provided options |
Random Sampling: To ensure results are 'fair' and representative of the whole population, participants must be selected randomly. Selecting only a specific group (e.g., only people at a gym to ask about national fitness) introduces bias.
Sample Size: The reliability of the data increases with the number of respondents. A small sample size may not capture the diversity of the population, leading to skewed results.
Pilot Testing: Before full distribution, a questionnaire should be tested on a small group to identify confusing questions or technical errors in the response options.
Check for Overlap: When critiquing a questionnaire in an exam, always look for numbers that appear in two different boxes (e.g., 10-20 and 20-30).
Look for Time Frames: If a question asks 'how often' but doesn't say 'per week' or 'per month', it is technically flawed and should be criticized.
Identify Bias: Check if the sample group is representative. If a survey about school food only asks the students in the cooking club, the sample is biased.
Verify Exhaustiveness: Ensure there is a '0' option if applicable and an 'Other' or 'More than...' option to catch outliers.
