Survey — Survey Research

Sample size depends on the desired margin of error, confidence level, expected effect size, and analysis plan. For descriptive surveys estimating a proportion, the standard formula is n = z²p(1-p)/e², where z is the z-score for the confidence level, p is the estimated proportion, and e is the margin of error. For analytical surveys testing relationships, an a priori power analysis based on the planned statistical test is preferable. Online calculators (e.g., G*Power) automate these calculations. Convenience-sample sizes common in student research (100–300) are often underpowered for subgroup analyses.

There is no universal threshold. Online surveys commonly achieve 20–40%, mail surveys 50–60%, and telephone surveys have declined sharply. The more important question is whether non-response is random or systematic. Even a 20% response rate may be acceptable if you can demonstrate that respondents do not differ from non-respondents on key variables; conversely, a 70% response rate is still problematic if the missing 30% are systematically different.

Yes, and this is common practice. Closed items yield quantifiable data; open-ended items add contextual depth and allow unexpected responses. However, open items increase completion time substantially and generate text data that must be coded qualitatively. Limit open items to the constructs where fixed options genuinely cannot capture the range of responses.

Likert scales (typically 5 or 7 labelled response points) are easy to administer and score, and their psychometric properties are well understood. Visual analogue scales (continuous 0–100 lines) offer finer discrimination and are common in pain and health research. Likert scales suit most social and behavioural research; visual analogue scales are preferable when detecting small changes within individuals over time is the priority.

In a survey the respondent reads and self-completes the questionnaire without an interviewer present. In a structured interview the same fixed questions are delivered verbally by an interviewer. Surveys reach larger samples at lower cost; structured interviews achieve higher completion rates and can clarify confusing items but are more resource-intensive and introduce interviewer effects.