Table of Contents
Purpose and Function of a Lab Report
A lab report is a formal scientific document that communicates the design, execution, and interpretation of an experiment. Its purpose is not merely to record what happened — it is to demonstrate that you can situate a scientific question in the existing literature, design and execute a rigorous investigation, interpret your findings in relation to your hypothesis, and communicate all of this with the precision, structure, and objectivity that scientific writing demands.
At undergraduate level, lab reports are primarily assessed as demonstrations of scientific literacy — understanding of the experimental method, appropriate use of scientific conventions, and ability to reason from data to conclusions. The experimental findings themselves may be less important than the quality of the reasoning applied to them.
Students frequently apologise for or try to explain away null results (where the hypothesis is not supported). In scientific writing, a null result reported accurately and discussed thoughtfully is as valuable as a positive finding — sometimes more so. What matters is the quality of the experimental design, the accuracy of the data, and the rigour of the interpretation. Never fabricate or adjust data to match the expected result.
The IMRAD Structure
Lab reports follow the IMRAD structure: Introduction, Methods, Results, And Discussion. Each section has a specific function and specific conventions. Understanding each section's distinct purpose prevents the most common structural errors — most notably, inserting interpretation into the Results section or providing background information in the Discussion.
| Section | Answers | Typical proportion |
|---|---|---|
| Introduction | Why was this experiment done? What does the existing literature establish? What does this experiment test? | 15–20% |
| Methods | How was the experiment conducted? (Precisely enough for replication) | 20–25% |
| Results | What was observed and measured? (Data and observations, no interpretation) | 25–30% |
| Discussion | What do the results mean? How do they relate to the hypothesis and existing literature? | 25–35% |
Tense Conventions Across Sections
Tense in scientific writing is not arbitrary — it reflects whether you are describing past actions, established knowledge, or current findings. Tense inconsistency signals a lack of scientific writing literacy.
| Section / context | Tense | Rationale and example |
|---|---|---|
| Introduction — established scientific knowledge | Present | "Dopamine mediates reward pathways in the mesolimbic system." Established facts are stated in present tense. |
| Introduction — previous studies | Past or present perfect | "García et al. (2020) found / have shown that…" |
| Introduction — purpose of this study | Past | "This experiment aimed to test…" / "We hypothesised that…" |
| Methods — procedures performed | Past | "Samples were incubated at 37°C for 24 hours." |
| Results — data reported | Past | "The mean reaction time was 342 ms (SD = 47)." |
| Results — reference to figures/tables | Present | "Figure 1 shows the dose-response relationship." |
| Discussion — what your results show | Present (with past for specific data points) | "These results suggest that… / The reaction time observed (342 ms) is consistent with…" |
| Discussion — established principles invoked | Present | "Le Chatelier's principle predicts that…" |
The Passive vs. Active Voice Debate
Scientific writing has a long tradition of passive voice use — "the solution was heated," not "we heated the solution" — grounded in the ideal of impersonal, reproducible science. However, many journals and institutions now explicitly permit or encourage active voice, particularly in the Discussion section, where the author's reasoning is foregrounded.
The principled position is this: use passive voice where the action matters more than the actor (Methods, Results), and active voice where the author's reasoning is the subject (Discussion conclusions, Introduction argument).
Always check your institution's or target journal's guidelines. At undergraduate level, consistent use of either voice is more important than the choice between them.
Writing the Introduction
The lab report introduction has three sequential tasks: establish the theoretical and empirical context; identify what is unknown or contested; state the hypothesis and experimental rationale. This is a compressed version of a research paper introduction and should be proportionately brief — typically 200–400 words for an undergraduate report.
Establish the background
What do we know from existing research about the phenomenon under investigation? Cite primary sources (journal articles) rather than textbooks wherever possible. State the relevant theory or mechanism.
Identify the gap or question
What is the specific aspect this experiment addresses? This does not need to be an original research gap — at undergraduate level, it is sufficient to explain what the experiment is designed to test or demonstrate.
State the hypothesis
A hypothesis must be precise and falsifiable: "It is hypothesised that increasing temperature from 25°C to 45°C will increase the rate of the catalase reaction, as measured by the rate of oxygen production, up to the enzyme's denaturation point." Avoid vague statements: "The experiment will show how temperature affects enzyme activity."
Writing the Methods Section
The methods section has a single, demanding criterion: sufficient detail for another competent researcher to replicate the experiment exactly. This means specifying equipment models, reagent concentrations, sample sizes, procedure steps, and any controls or randomisation procedures.
A common error is writing the methods as a recipe: "Mix 10ml of solution A with 5ml of solution B." The correct form is past-tense passive: "10 ml of solution A was combined with 5 ml of solution B." The methods section reports what was done, not what to do.
Methods sections should also identify: the independent and dependent variables; any controlled variables and how they were controlled; the sample size and any inclusion/exclusion criteria; the statistical analysis planned and performed. Ethical approval should be noted for research involving human participants.
Narrating Results
The results section is where the distinction between reporting and interpreting is tested. Results are presented objectively: what was measured, what values were obtained, what statistical tests were applied and what they showed. Interpretation — what this means, whether it supports the hypothesis, why it might have occurred — belongs in the Discussion.
The three-part results sequence
- Signal the key finding — "The mean response rate in the experimental condition was significantly higher than in the control condition."
- Provide the evidence — numerical data with appropriate precision, statistical test result, significance level, and effect size: "M = 47.3 (SD = 8.2) vs M = 31.6 (SD = 7.9); t(58) = 7.42, p < .001, d = 1.91."
- Refer to the visual — "Figure 2 presents the dose-response curve for all four treatment groups." Do not describe figures in full in the text — the figure exists for that purpose.
The Six-Point Discussion Structure
The Discussion is the most intellectually demanding section of a lab report. It requires you to reason from your specific findings toward broader scientific understanding. The following six-point structure covers everything a strong discussion must accomplish.
State whether the hypothesis was supported
Open directly: "The results support / do not support the hypothesis that…" Do not keep the reader guessing. Precise reference to the key finding is appropriate here.
Interpret the key finding
What do the results mean mechanistically or theoretically? Explain why you obtained the results you did, drawing on the theoretical framework established in the Introduction.
Compare with existing literature
Are your results consistent with prior studies? If they differ, propose a plausible explanation for the discrepancy (methodological differences, sample characteristics, context). This is where citations from the Introduction are reactivated.
Identify and analyse limitations
What aspects of the experimental design may have affected the validity or reliability of the findings? Sample size constraints, uncontrolled confounds, measurement precision, ecological validity. Note that limitations are analytical acknowledgements — not excuses for poor results.
Suggest future research directions
Based on the limitations and the findings, what would the next logical experiment be? Speculative but grounded — the suggestion should follow logically from the analysis.
Conclude
A brief, precise conclusion restating the main finding and its significance. This is usually a single paragraph and should not introduce new information.
Figures, Tables, and Visual Data
Figures and tables are not decorative — they are data in visual form. Both must be numbered, titled, and captioned so that they are self-explanatory without reference to the main text.
- Tables present precise numerical data; titles appear above the table in most APA/scientific formats.
- Figures (graphs, photographs, diagrams) present trends and relationships; captions appear below the figure.
- Refer to every figure and table in the text — an unreferenced visual is invisible. Do not present the same data in both a table and a figure.
- Axes must be labelled with units. Bar charts require error bars (SD or SEM) for quantitative data. Legends must be present for multi-series graphs.
Section-by-Section Errors
| Section | Common error | Correct approach |
|---|---|---|
| Introduction | Hypothesis stated vaguely or omitted | A precise, falsifiable hypothesis is required: state the direction of the predicted effect and the measured variable |
| Methods | Written as instructions ("Add 10 ml…") | Use past tense passive: "10 ml was added…" |
| Methods | Statistical analysis not described | State which test was used, and the significance threshold applied (typically α = 0.05) |
| Results | Interpretation mixed with findings | Report what was found; reserve explanation of why for the Discussion |
| Results | Data reported only in figures — not narrated | Every key finding should be narrated in prose; figures supplement, not replace, the text |
| Discussion | Hypothesis support/rejection not stated clearly | The first sentence of the Discussion should explicitly state whether the hypothesis was supported |
| Discussion | No engagement with prior literature | At least 2–3 citations comparing or contextualising your findings are expected |
| Discussion | Limitations treated as apology | Identify specific methodological limitations and explain their effect on the validity of conclusions |