What type of study is it when a new safe drinking water chlorination intervention is introduced in one village to reduce the incidence of typhoid fever, while a nearby village serves as a comparison?

Study Classification: Community Trial

This study is best classified as a community trial (option c), where an intervention is implemented at the community/village level with entire populations serving as the units of allocation and comparison.

Rationale for Classification

Key Distinguishing Features

• Unit of allocation is the community: The intervention (water chlorination) was assigned to an entire village, not to individual participants, making this a cluster-based design 1

• Population-level intervention: Safe drinking water chlorination affects all residents of the village simultaneously, representing a community-wide environmental modification rather than individual-level treatment 2

• Non-randomized allocation: The question does not indicate random assignment of villages to intervention versus control conditions, which distinguishes this from a randomized controlled trial 2

• Comparison village serves as control: A nearby village with similar characteristics provides the comparison group, typical of community trial methodology 1

Why Other Options Are Incorrect

Not a Randomized Controlled Trial (Option a)

• Lacks individual randomization: RCTs require random allocation of individual participants to intervention or control groups 1
• No mention of randomization process: The scenario describes selection of villages but does not specify random assignment 1

Not a Field Trial (Option b)

• Field trials target individuals: Field trials typically involve individual-level interventions (like vaccines) delivered to people at high risk in community settings, with individual participants as the unit of analysis 2
• Different intervention level: While field trials occur in community settings, they randomize and intervene at the individual level, not the community level 3

Not an Ecological Study (Option d)

• Ecological studies lack intervention: Ecological studies are observational, examining associations between population-level exposures and outcomes without implementing an intervention 2
• This study is experimental: The deliberate introduction of chlorination represents an experimental intervention, not passive observation 3

Community Trial Characteristics Present

• Geographic clustering: Villages serve as natural clusters where residents share the same water supply 1

• Contamination prevention: Community-level allocation prevents contamination that would occur if some individuals within a village received chlorinated water while others did not 2

• Public health intervention: Water chlorination represents a classic environmental public health measure targeting disease prevention at the population level 1

• Feasibility considerations: Implementing water chlorination at the village level is administratively and logistically more feasible than individual-level allocation 2, 3

Important Methodological Considerations

• Statistical analysis implications: The village (not individuals) should be the unit of analysis, requiring appropriate methods that account for intracluster correlation 1

• Sample size requirements: Community trials require fewer clusters but larger overall sample sizes compared to individually randomized trials due to clustering effects 1

• Generalizability: Results apply to similar communities with comparable population characteristics and risk factors 1, 2