---
name: experimental-design
title: Choose a Method and Design a Study Around Its Question
description: Match a research question to a method that can answer it, state the method as a falsifiable procedure with its assumptions and scope, and design the study (variables, controls, sample size, acceptance criterion, confounds) before data is collected.
keywords:
- level:L0
- methodology
- study-design
---

## Choose the method

Start from what the question asks (a mechanism, a comparison, a prediction, a
characterization) and choose a method that can produce evidence for that
claim, not just a familiar one. State it as a falsifiable procedure: which
result would support the hypothesis, and which would weaken or contradict it.

Name the method's assumptions and scope: the population, system, regime and
conditions it applies to, and what it does not cover. A method borrowed from
an adjacent field or a different system needs justification before its
validity transfers.

Keep the method separate from the instrument, program or protocol that
executes a step of it, so the method survives a tool change.

## Design the study

- **What it must distinguish.** State the hypothesis, the independent
  variables changed, the dependent variables measured, and every variable
  held constant or controlled. An uncontrolled variable that correlates with
  the one of interest invalidates the comparison however the data is analysed
  afterwards.
- **Size.** State the number of replicates needed to detect the effect of
  interest given the expected scatter, not a convenient or traditional number.
- **Acceptance criterion, fixed in advance.** For a comparison, define what
  counts as a difference before collecting data; choosing it after seeing the
  results does not test the hypothesis.
- **Confounds.** Identify batch, location, operator, instrument and time
  effects, and design to detect or exclude them: randomization, blocking,
  replication across batches.

## Return

The method with its assumptions, scope and falsification criteria; the study
design (hypothesis, variables and controls, sample size and rationale,
acceptance criterion, confound controls); and the specialists or skills
needed for each step.