Why English? | Reading ARRIVE 2.0 Animal Research Reports Through Study Design, Sample Size, Welfare and Results

People searching for ARRIVE 2.0 guidelines, animal research reporting or the ARRIVE Essential 10 often need help separating study design from biological measurements. English matters because a reader must distinguish animal, cage, litter and measurement as possible units; follow allocation and blinding; understand procedures and welfare monitoring; and connect results to the animals and conditions actually studied.

The official ARRIVE 2.0 site, checked on 5 November 2026, organises the guidance into two prioritised sets. The ARRIVE Essential 10 are the minimum items needed for readers and reviewers to assess reliability. The Recommended Set adds context and best-practice reporting. The official materials identify the Essential 10 as study design, sample size, inclusion and exclusion criteria, randomisation, blinding, outcome measures, statistical methods, experimental animals, experimental procedures and results.

ARRIVE 2.0 supports transparent reporting of in vivo animal research. It does not replace ethical and legal oversight, justify animal use, certify humane conduct or guarantee translation to people. This article keeps welfare and scientific inference together while respecting the stated priority of the Essential 10.

---

Map Every Experimental Group

ARRIVE Essential 10 begins with study design because the comparison must be visible.

Study record

Identify experimental and control groups, the intervention or exposure and the unit receiving it. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A diagram distinguishes four diet-by-treatment groups and states why no sham group was used.

Welfare and inference

A named control is only useful if its conditions are described. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Redraw the group structure before interpreting outcomes. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Identify the Experimental Unit

The experimental unit is the smallest entity independently allocated to a condition.

Study record

Look for animal, litter, cage, tank or another unit and distinguish it from the measurement unit. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

Ten measurements from each of six cages do not create sixty independent experimental units.

Welfare and inference

Confusing units can produce false precision. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Match allocation, analysis and sample-size claims to the true unit. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Explain the Exact Sample Size

Reports should state the number of experimental units in every group.

Study record

Find planned and analysed numbers and any repetition of experiments. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A study lists eight animals per group, two technical measurements per animal and one independent replication cohort.

Welfare and inference

Technical replicates do not replace biological replication. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Keep animals, units and measurements in separate columns. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Justify the Sample-Size Calculation

The calculation reveals the target effect, variability, power and error assumptions.

Study record

Look for the outcome used, expected effect, variance source and allowance for loss. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

The primary outcome drives the calculation, while secondary exploratory measures do not receive separate power claims.

Welfare and inference

A calculation based on optimistic pilot variance may still be underpowered. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Compare assumptions with the observed data and exclusions. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Define Inclusion and Exclusion Criteria

Criteria should be established before outcomes are inspected where possible.

Study record

Find rules for animals, units and data points and whether they were prespecified. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A physiological-quality threshold is set before analysis and applied without knowledge of group assignment.

Welfare and inference

Flexible exclusions can change results. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Record each rule, timing and number affected. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Report Every Exclusion

Readers need a transparent account of animals or observations removed from analysis.

Study record

Look for reasons and group membership, including a statement when none were excluded. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

One animal is excluded after a prespecified equipment-failure rule; the report retains it in the flow account.

Welfare and inference

A plausible reason can still create imbalance. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Check whether conclusions change under reasonable alternative handling. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Describe Randomisation

Randomisation can reduce systematic allocation differences when properly implemented.

Study record

Find the sequence method, unit, blocking or stratification and implementation. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A computer-generated blocked sequence balances sex while a separate person conceals allocation.

Welfare and inference

The word random without a method is insufficient. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Trace sequence generation, concealment and actual assignment. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Control Confounders Such as Order and Location

Order, cage position, processing batch and time can become hidden group differences.

Study record

Look for randomisation or balancing across these conditions. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

Sample processing order is randomised within day so treatment is not perfectly aligned with instrument drift.

Welfare and inference

Balancing one factor does not remove every confounder. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. List operational variables that could travel with group assignment. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Report Blinding at Each Stage

Blinding can apply during allocation, procedure, outcome assessment and analysis.

Study record

Find who knew group identities at each stage and why blinding was not feasible where relevant. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

Technicians know treatment during dosing, but outcome images are relabelled before scoring.

Welfare and inference

Blinding cannot prevent all measurement bias and may be broken. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Create a stage-by-stage knowledge table. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Name Primary and Secondary Outcomes

Outcomes need definitions, timing and measurement methods.

Study record

Identify the primary outcome used for the sample-size calculation and distinguish secondary or exploratory measures. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

The report specifies locomotor activity at day seven as primary and biomarker panels as secondary.

Welfare and inference

Choosing the most favourable result after analysis inflates evidence. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Compare outcome labels with the protocol or registration. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Describe Statistical Methods

Analysis should match design, unit and outcome distribution.

Study record

Look for models, factors, repeated measures, clustering, transformations and multiple-comparison handling. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A mixed model includes cage as a random effect and time as a repeated factor.

Welfare and inference

Statistical complexity cannot rescue weak allocation or measurement. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Map each method to a named outcome and unit. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Check Assumptions

ARRIVE asks how assumptions were assessed.

Study record

Find checks for distribution, variance, model fit and influential observations. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

Residual plots reveal unequal variance, so the team uses an appropriate robust analysis and reports the change.

Welfare and inference

A non-significant normality test does not prove normality. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Read graphical and substantive diagnostics together. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Describe Species, Strain and Substrain

Animal characteristics can materially affect biology and replication.

Study record

Find species, strain, substrain and relevant genetic modification or health status. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

The report names a substrain because metabolic phenotypes differ across closely related lines.

Welfare and inference

A strain label may still hide supplier or colony differences. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Attach biological claims to the described animals. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Report Sex, Age and Weight

Sex, developmental stage and size can change response and welfare needs.

Study record

Look for values at relevant experimental times and the rationale for restrictions. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A study using only males explains the scientific reason and avoids generalising to both sexes.

Welfare and inference

Adding both sexes without adequate design may not support sex-specific conclusions. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. State the represented population and the boundary. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Name Source and Health Status

Supplier, breeding history and pathogen status can influence results.

Study record

Find source, colony, import, acclimatisation and health information. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

Animals arrive from two suppliers, so supplier is balanced across groups and reported.

Welfare and inference

Commercial sourcing does not guarantee equivalence. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Track source as a potential contextual variable. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Describe Experimental Procedures

Procedures must be reproducible and understandable for welfare review.

Study record

Report what was done, how, when, where and by whom, including anaesthesia, analgesia and routes. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A dosing procedure states formulation, volume, route, time of day and operator training.

Welfare and inference

A protocol citation may refer to a different version or omit local modifications. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Give the exact procedure used and link stable supporting detail. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Explain Why Procedures Were Chosen

A rationale connects procedure, dose and timing to the scientific question.

Study record

Look for evidence, pilot work or practical constraints behind key choices. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

The sampling time is selected to capture a predicted peak rather than because it is convenient.

Welfare and inference

A rationale does not make a harmful or biased procedure acceptable. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Separate scientific purpose from ethical approval and feasibility. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Report Housing and Husbandry

Environment can change physiology, behaviour and stress.

Study record

Find cage or tank type, density, bedding, light cycle, temperature, enrichment, food and water. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

The study reports group housing and nesting material because both may influence social behaviour.

Welfare and inference

Standard conditions differ across facilities. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Identify environmental features likely to interact with the outcome. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Describe Acclimatisation

Transport and new environments can affect measurements.

Study record

Look for acclimatisation duration, handling and any quarantine. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

Animals acclimatise for seven days and receive the same handling routine before baseline testing.

Welfare and inference

A fixed duration does not prove stress has resolved. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Connect timing to the measured biology. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Explain Animal Care and Monitoring

Monitoring protects welfare and can explain attrition or altered outcomes.

Study record

Find frequency, indicators, humane endpoints and actions taken. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A severity score triggers analgesia, veterinary review or early euthanasia under prespecified rules.

Welfare and inference

Monitoring language is weak without thresholds and responses. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Record who assessed, how often and what each threshold caused. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Report Adverse Events

Unexpected harm affects welfare, interpretation and reproducibility.

Study record

Look for event type, frequency, group, response and a statement when none occurred. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

Two procedure-related injuries lead to a technique change that is dated and described.

Welfare and inference

Not every event is caused by the experimental condition. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Separate observation, attribution and response. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Present Results With Summary and Variability

ARRIVE asks for results for each experiment and group.

Study record

Find descriptive statistics, effect estimates and variability with clearly defined units. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A figure reports mean difference with a confidence interval and individual animal points.

Welfare and inference

A p-value alone does not show size or uncertainty. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Read effect, precision, distribution and exclusions together. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Show Exact Numbers Analysed

Every result needs the number of experimental units included.

Study record

Check that n is defined and consistent across text, tables and figures. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A caption states n equals cages rather than total animals because allocation occurred by cage.

Welfare and inference

Changing denominators can signal missing data or pseudoreplication. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Annotate each outcome with its true n and reason for loss. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Interpret Findings in Light of Objectives

The discussion should answer the stated objective without outrunning design.

Study record

Look for biological interpretation, uncertainty and alternative explanations. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

The authors describe association in an observational component rather than claiming that the exposure caused the outcome.

Welfare and inference

Statistical significance is not biological importance. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Restate the conclusion using the design’s strongest warranted verb. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Discuss Limitations and Bias

Limitations should cover design, implementation, measurement and analysis.

Study record

Find constraints such as small samples, unblinded procedures, single sex, attrition or facility effects. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

The team notes that allocation was random but outcome assessment could not be blinded and explains the direction of possible bias.

Welfare and inference

Disclosure does not erase the limitation. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Translate the limitation into a boundary on the claim. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Consider Generalisability and Translation

Animal findings may depend on species, model and experimental conditions.

Study record

Look for cautious discussion of relevance to other animals, environments or human biology. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A disease model captures one mechanism but not the full clinical condition, so the authors frame human relevance as a hypothesis.

Welfare and inference

Animal evidence alone cannot promise human benefit. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Name the biological bridge and the uncertainties across it. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Verify Ethics, Protocol Registration and Data Access

The Recommended Set adds transparency around approval, planning and reusable evidence.

Study record

Find the ethical body and identifiers, protocol registration where used, data location and restrictions. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A report links a preregistration and a repository containing anonymised outcome data and analysis code.

Welfare and inference

Approval, registration and sharing each solve different problems. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Check dates, version alignment and stated access conditions. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Read Interests and Funding

Relationships and resources can shape design, materials and interpretation.

Study record

Find competing interests, funding source and funder role. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A device manufacturer supplies equipment, while allocation, analysis and publication decisions remain with investigators.

Welfare and inference

Disclosure enables scrutiny but does not determine validity. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Connect the support to decisions it could plausibly affect. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Use the Essential 10 Before the Recommended Set

ARRIVE 2.0 deliberately prioritises a minimum reliability set before broader context.

Study record

Audit study design, sample size, criteria, randomisation, blinding, outcomes, statistics, animals, procedures and results first. ARRIVE 2.0 makes the experimental unit, allocation, animals, procedures and results visible enough for readers to assess reliability. The item belongs to a connected record; it should not be read as an isolated box.

A student completes an Essential 10 table before reading background claims, then adds Recommended Set context.

Welfare and inference

Priority does not make the Recommended Set optional for best reporting. Transparent reporting supports ethical scrutiny and scientific interpretation, but it does not itself approve the study, prove humane practice or guarantee translation to people. Use both sets while preserving their different functions. Write a short audit note that separates what the report states, what the design permits readers to infer and what remains unknown.

---

Frequently Asked Questions

What is ARRIVE 2.0?

It is updated reporting guidance for research involving animals, organised into the Essential 10 and a Recommended Set.

What are the Essential 10?

They cover study design, sample size, criteria, randomisation, blinding, outcomes, statistics, animals, procedures and results.

What is an experimental unit?

It is the smallest unit independently allocated to an experimental condition.

Why can cage and animal numbers differ?

Animals sharing a cage may receive an intervention together, making the cage rather than each animal the independent unit.

Does randomisation prove there is no bias?

No. The method, implementation, concealment and later measurement still matter.

Is blinding always possible?

Not always. Reports should state who was blinded at each stage and explain unavoidable knowledge.

Why report housing?

Light, temperature, enrichment, density and other environmental features can affect biology and welfare.

Does ethical approval guarantee good reporting?

No. Approval and reporting transparency are related but distinct responsibilities.

Can animal findings promise benefit for humans?

No. Translation requires additional evidence and careful reasoning about biological relevance.

How should a student start?

Identify groups and experimental units, then audit the Essential 10 before adding Recommended Set context.

---

Useful Next Reading

• Read the official ARRIVE 2.0 guidance.
• Download the official ARRIVE author checklists.
• Compare experimental reporting with CONSORT 2025 trial reports.
• Practise explaining scientific evidence without overclaiming.

Closing thought: ARRIVE 2.0 is most useful when a reader can trace every result back to the correct experimental unit, the animals and procedures involved, and the welfare and design conditions that bound the conclusion.