Experimental Designs
Randomised Controlled Trials (RCTs)
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Participants are randomly assigned to intervention or control groups.
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Aim to test the efficacy or safety of interventions while minimising bias.
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Considered the gold standard for evaluating treatments in clinical research.
Clinical Trials
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Studies involving human volunteers to assess the effects of interventions (can include RCTs, phase I-IV drug trials, etc.).
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Typically involve a protocol specifying inclusion/exclusion criteria, interventions, and outcomes.
Preclinical Studies
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Conducted before human trials, often using cell cultures or animal models.
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Assess safety, pharmacology, and biological activity of potential interventions.
Observational Designs
Cohort Studies
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Follow a group with shared characteristics (the cohort) over time to assess the impact of exposures on outcomes.
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Can be prospective (looking forward) or retrospective (looking back at existing records).
Case-Control Studies
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Compare individuals with a specific outcome (cases) to those without (controls) to identify risk factors.
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Usually retrospective.
Cross-Sectional Studies
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Assess both exposure and outcome at a single point in time in a defined population.
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Useful for estimating prevalence.
Case Reports
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Detailed descriptions of a single patient or small group with a unique or rare condition.
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Often used to highlight new diseases or adverse drug reactions.
Longitudinal Studies
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Track participants over a period to observe outcomes and changes over time.
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Can be either observational (e.g., cohort studies) or experimental.
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Useful for studying development, risk factors, and disease progression.
Descriptive Studies
Surveys
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Structured questionnaires to collect data on behaviours, experiences, or attitudes from a sample.
Qualitative Research
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Explores experiences, opinions, or behaviours using interviews, focus groups, or thematic analysis.
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Data are non-numeric and provide depth and context.
Data Collection Methods
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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
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NHS Health Research Authority, “Types of research studies”
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Royal Pharmaceutical Society, “Research and Evaluation in Pharmacy Practice”
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British National Formulary, “Introduction to Clinical Trials”
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NICE, “Methods for the development of NICE public health guidance”