Experimental Designs
Randomised Controlled Trials (RCTs)
Participants are randomly assigned to intervention or control groups.
Aim to test the efficacy or safety of interventions while minimising bias.
Considered the gold standard for evaluating treatments in clinical research.
Clinical Trials
Studies involving human volunteers to assess the effects of interventions (can include RCTs, phase I-IV drug trials, etc.).
Typically involve a protocol specifying inclusion/exclusion criteria, interventions, and outcomes.
Preclinical Studies
Conducted before human trials, often using cell cultures or animal models.
Assess safety, pharmacology, and biological activity of potential interventions.
Observational Designs
Cohort Studies
Follow a group with shared characteristics (the cohort) over time to assess the impact of exposures on outcomes.
Can be prospective (looking forward) or retrospective (looking back at existing records).
Case-Control Studies
Compare individuals with a specific outcome (cases) to those without (controls) to identify risk factors.
Usually retrospective.
Cross-Sectional Studies
Assess both exposure and outcome at a single point in time in a defined population.
Useful for estimating prevalence.
Case Reports
Detailed descriptions of a single patient or small group with a unique or rare condition.
Often used to highlight new diseases or adverse drug reactions.
Longitudinal Studies
Track participants over a period to observe outcomes and changes over time.
Can be either observational (e.g., cohort studies) or experimental.
Useful for studying development, risk factors, and disease progression.
Descriptive Studies
Surveys
Structured questionnaires to collect data on behaviours, experiences, or attitudes from a sample.
Qualitative Research
Explores experiences, opinions, or behaviours using interviews, focus groups, or thematic analysis.
Data are non-numeric and provide depth and context.
Data Collection Methods
Can include interviews, questionnaires, observations, or review of existing records.
Prospective vs Retrospective Study Designs
| Aspect | Prospective | Retrospective |
|---|---|---|
| Timing | Follows participants into the future | Looks back at existing data |
| Data Collection | Data collected as events happen | Data collected from past records |
| Example | Cohort studies, RCTs | Case-control studies |
Strengths and Limitations of Study Designs
| Study Design | Strengths | Limitations |
|---|---|---|
| RCTs | High internal validity, minimises bias | Expensive, time-consuming, strict criteria may limit generalisability |
| Clinical Trials | Structured, regulated, reliable outcomes | Can be costly and complex |
| Preclinical | Identifies safety before human exposure | Results may not translate to humans |
| Cohort Studies | Good for studying multiple outcomes | Potential for confounding, can be costly if prospective |
| Case-Control | Efficient for rare outcomes, quick | Recall bias, cannot calculate incidence |
| Cross-Sectional | Quick, inexpensive, good for prevalence | Cannot establish causality |
| Case Reports | Identify novel phenomena | Cannot infer causation, very limited sample size |
| Surveys | Gather broad data quickly | Subject to response bias |
| Qualitative | Rich, in-depth understanding | Subjective, hard to generalise |
References
NHS Health Research Authority, “Types of research studies”
Royal Pharmaceutical Society, “Research and Evaluation in Pharmacy Practice”
British National Formulary, “Introduction to Clinical Trials”
NICE, “Methods for the development of NICE public health guidance”