A postgraduate student wants to answer the research question: “Does exclusive breastfeeding reduce the risk of eczema in infants?” She creates a strict search strategy with predefined inclusion and exclusion criteria, screens multiple databases, and critically appraises all included studies. What type of study is she conducting?
一名研究生想要回答研究问题：“纯母乳喂养是否能降低婴儿湿疹的风险？” 她制定严格的检索策略，预设纳入和排除标准，筛选多个数据库，并对所有纳入的研究进行批判性评估。她正在进行什么类型的研究？

Question

BlackTom AI · Accepted Answer

A systematic review is a structured, reproducible synthesis of research evidence that uses a predefined protocol, exhaustive searches of multiple databases, explicit inclusion/exclusion criteria, and critical appraisal of included studies — all features described in the vignette.

1) Relevant knowledge points and concepts
- Systematic review: a rigorous literature review following a protocol (often registered), with comprehensive database searches, study selection based on preset criteria, and critical appraisal of study quality (e.g., using risk-of-bias tools). Reporting guidelines include PRISMA.
- Meta-analysis: a statistical technique that can be part of a systematic review to quantitatively pool results across studies; not every systematic review performs a meta-analysis.
- Cohort study: a primary observational study that follows groups defined by exposure over time to measure outcomes.
- Cross-sectional study: a primary study that measures exposure and outcome at a single time point in a population.

2) Step-by-step reasoning
Step 1 — Identify actions in the scenario: creation of a strict search strategy, predefined inclusion/exclusion criteria, screening multiple databases, and critical appraisal of all included studies. These are hallmarks of a literature synthesis process done according to a protocol.
Step 2 — Match these actions to study types:
- They are not collecting new participant data over time, so it is not a cohort study.
- They are not taking a single-time measurement from participants, so it is not a cross-sectional study.
- They are synthesizing existing studies with systematic search and appraisal — this matches a systematic review.
Step 3 — Consider meta-analysis: although meta-analysis involves statistical pooling of study results, the vignette does not mention combining data quantitatively. Therefore the correct label is systematic review (which may or may not include meta-analysis).

3) Why the correct answer is correct
The described methodology (predefined protocol, exhaustive database search, eligibility criteria, and critical appraisal) is the defining process of a systematic review. The absence of any mention of original data collection excludes cohort and cross-sectional designs.

4) Why other options are incorrect
- Meta-analysis: possible component of a systematic review but requires statistical pooling; the vignette does not state pooling was performed.
- Cohort study and Cross-sectional study: both are primary research designs involving direct data collection from participants, which is not what the student is doing.

Conclusion: The student is conducting a systematic review — this matches the provided correct answer.

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