Research Gap

A research gap is an area within the existing body of literature where knowledge is incomplete, contradictory, outdated, or entirely absent, indicating that further investigation is needed. Identifying a research gap establishes the justification for conducting a new study and positions the proposed research within the broader scholarly conversation.

A well designed study begins with a clear identification of what is not yet known. The research gap provides the rationale for the study: it explains why the research question matters, why existing evidence is insufficient, and what new knowledge the proposed study will contribute. Grant reviewers, journal editors, and thesis committees all evaluate whether a research gap has been convincingly identified and whether the proposed study is positioned to address it. Without a clearly articulated gap, research risks being redundant, unfocused, or irrelevant to the needs of the field.

Research gaps are identified through comprehensive literature reviews, systematic reviews, and scoping reviews. Evidence and gap maps, described by Snilstveit and colleagues in 2016, lay out the available studies or reviews in a grid of interventions and outcomes, so that empty or sparse cells show where evidence is missing. The process involves searching the literature on a topic, synthesizing existing evidence, and identifying areas where the evidence is lacking. Gaps can take several forms, and published typologies differ: Müller-Bloch and Kranz (2015), for example, distinguish contradictory evidence, knowledge void, action knowledge conflict, methodological, evaluation void and theory application void gaps. One practical grouping follows.

Empirical gaps exist when a research question has not been studied at all, or when existing studies have not examined specific populations, settings, or outcomes. For example, a drug may have been tested in adults but not in children, creating a population gap.

Methodological gaps arise when existing studies on a topic suffer from design limitations that weaken the evidence. If all studies of a particular intervention are pre post designs without control groups, there is a gap in causal evidence that a randomized trial could fill.

Theoretical gaps occur when existing theories do not fully explain observed phenomena, or when competing theories make different predictions that have not been tested.

Conflicting evidence represents a gap when studies produce contradictory results that have not been reconciled through replication, meta analysis, or investigation of moderating factors.

Knowledge synthesis gaps exist when primary studies are available but have not been systematically synthesized, preventing the field from drawing reliable conclusions.

Documenting the gap requires more than stating that "no study has examined X." A convincing gap analysis explains why the missing knowledge matters, who needs it, and how the proposed study is designed to address it. It places the gap in context, showing how it relates to clinical practice, policy needs, or theoretical development.

Identify the research gap during the early stages of study planning, typically as part of the literature review that precedes protocol development. Use it to frame the research question, justify the study's significance, and guide the study design. In grant applications, the research gap is typically presented in the introduction or significance section. In journal manuscripts, it appears in the introduction as the transition from the literature review to the research question and objectives.

A common error is overstating the gap by claiming that "nothing is known" about a topic when relevant research exists but has not been thoroughly reviewed. Another mistake is identifying a gap that is too narrow or too obscure to justify a new study, producing research that will have minimal impact. Researchers sometimes identify gaps that are not addressable with available methods or resources, leading to poorly designed studies. Finally, failing to update the literature review before data collection may mean that the identified gap has been filled by studies published in the interim.

A scoping review of interventions for medication adherence in heart failure identifies 45 published trials. The review finds that nearly all studies were conducted in high income countries, enrolled predominantly male participants, and followed patients for no more than six months. The authors identify three gaps: (1) trials in low and middle income countries are almost absent, where heart failure burden is growing rapidly; (2) women are underrepresented, limiting generalizability; and (3) adherence beyond six months has rarely been studied. These gaps provide the justification for a new multicenter trial in three sub Saharan African countries with a 12 month follow up and stratified enrollment targeting 50% female participation.