What is Amidakuji? Understanding Japan's Fair Decision-Making Method

Amidakuji is a traditional Japanese lottery method that has been used for fair and transparent selection for generations. With just paper and a pen, anyone can create a selection system that's mathematically guaranteed to be fair.

This article will explore the fundamentals of amidakuji, its history, and how it's being used in the modern world.

What is Amidakuji?

The Basics

Amidakuji (阿弥陀籤) is a lottery method that uses a diagram of vertical and horizontal lines to fairly distribute outcomes among participants.

Basic Structure:

• Vertical lines: One for each participant
• Horizontal lines: Random "rungs" connecting adjacent vertical lines
• Start points: Top of the vertical lines
• End points: Results placed at the bottom of each line

Origin of the Name

The name "amidakuji" comes from its resemblance to the halo of Amida Buddha. When the paper is folded into a fan shape, it resembles the radiant halo seen in Buddhist iconography.

Names Around the World

Similar methods are used in other countries with unique names:

• Japan: Amidakuji (阿弥陀籤)
• Korea: Sadaritagi (사다리타기, "ladder climbing")
• China: Guijiaotu (鬼腳圖, "ghost leg diagram")
• English: Ghost Leg, Ladder Lottery

This method is particularly popular across Asia for fair decision-making.

How Amidakuji Works

Basic Rules

1. Setup: Draw vertical lines equal to the number of participants
2. Create rungs: Connect vertical lines with horizontal lines randomly
3. Choose start: Each participant selects a starting point at the top
4. Trace path: Follow the chosen line from top to bottom
   • When you encounter a horizontal line, you must follow it
   • Return to a vertical line and continue downward
   • Repeat until reaching the bottom
5. Confirm result: The outcome at the bottom is your result

The Secret of Fairness

Amidakuji is fair because of its mathematical properties:

Guaranteed 1:1 Correspondence

• Every start point leads to a different end point
• No two people will reach the same destination
• No destination will be left unassigned

Unpredictability

• Even a few horizontal lines create complex, hard-to-predict paths
• The human brain cannot instantly calculate the result
• Fair and transparent selection is achieved

Comparing Amidakuji to Other Methods

For a detailed comparison of lottery methods, see Lottery Method Comparison.

Random Drawing

Problems:

• Multiple winners for the same prize may occur
• Some outcomes may never be selected
• Not a perfect 1:1 match

Amidakuji Advantages:

• Everyone gets a unique result
• No duplicates or omissions

Rock-Paper-Scissors

Problems:

• Ties can occur
• May require multiple rounds
• Not suitable for large groups

Amidakuji Advantages:

• Decides everything in one round
• Works for large groups (up to 299 people)
• No need for retries

Roulette / Lottery Apps

Problems:

• The mechanism is hidden, raising trust concerns
• Possibility of manipulation cannot be ruled out

Amidakuji Advantages:

• The entire process is visible
• Complete transparency that everyone can accept
• All participants contribute to randomness

How to Use Amidakuji

Step 1: Preparation

1. Prepare paper and pen
2. Draw vertical lines for the number of participants
3. Write results (prizes, roles, etc.) at the bottom

Step 2: Creating Rungs

Method 1: Concealed Creation

• Hide the results and draw horizontal lines
• Create with no one knowing the outcomes
• Most fair method

Method 2: Sequential Creation

• Each participant adds one horizontal line in turn
• Everyone equally contributes to randomness
• Highly transparent method

Step 3: Choose Start

Each participant selects their starting point at the top.

Step 4: Trace

Follow your chosen line from top to bottom, taking every horizontal line you encounter.

Step 5: Confirm Result

The result at your destination becomes your outcome.

Use Cases for Amidakuji

Role Assignment

• Selecting party organizers
• Assigning project roles
• Duty allocation
• MC selection

Event Lotteries

• Prize winner selection
• Raffle drawings
• Gift distribution
• Participation prize allocation

Team Division

• Group work team formation
• Sports team division
• Project team assignment
• Pair programming partner selection

Order Determination

• Presentation order
• Karaoke turn order
• Game play order
• Bill payment responsibility

Limitations of Traditional Amidakuji

Constraints of Paper Amidakuji

Location Constraints:

• All participants must be in the same place
• Remote participation is impossible
• Travel costs are required

Process Challenges:

• Need to coordinate the order of drawing lines
• Time-consuming
• Difficult to manage with large groups

Recording Issues:

• Results disappear unless photographed
• Difficult to share
• Hard to review later

The Emergence of Online Amidakuji

To solve these challenges, online amidakuji services have emerged. Learn more about offline vs online lottery methods.

Benefits of Online Version

Location Independence:

• Remote participation possible
• Access from anywhere in the world
• No travel required, saving time

Automatic Management:

• System automatically manages progress
• Real-time participation tracking
• Smooth operation

Recording and Sharing:

• Share results via URL
• Check results anytime
• No need for screenshots

Large Group Support:

• Up to 299 participants
• Suitable for large-scale events
• Almost no limit on participant numbers

Amida-san: Free Online Amidakuji

Amida-san is a service that lets you use amidakuji online for free.

Key Features

Completely Free:

• All basic features are free
• No registration required
• No personal information needed

Easy to Use:

• Just share the URL
• Compatible with smartphones, tablets, and PCs
• Optimized for touch operations

Fairness:

• Same mechanism as traditional amidakuji
• Transparent process
• Fair selection everyone can accept

Rich Features:

• Real-time participation
• 3D visualization (paid option)
• Multi-language support
• QR code sharing

How to Use

1. Visit Amida-san
2. Set event title and outcomes
3. Share URL with participants
4. Everyone adds horizontal lines
5. Execute lottery and check results

That's all it takes to achieve fair and transparent selection.

Frequently Asked Questions

Q1: Is amidakuji really fair?

Yes, it's mathematically proven. Every start point leads to a different end point, guaranteeing a 1:1 correspondence.

Q2: How many horizontal lines are needed?

There's no strict rule, but having 2-3 times the number of participants typically generates sufficiently random paths.

Q3: Does the online version maintain fairness?

Yes, Amida-san uses the same mechanism as traditional amidakuji, and the process where everyone adds lines is completely transparent.

Q4: Can results be changed afterward?

No, results cannot be changed after execution. This maintains fairness.

Q5: Does it work for large groups?

Yes, Amida-san supports up to 299 participants.

Summary

Amidakuji is a fair lottery method that has been used in Japan for generations:

• Simple mechanism requiring only paper and pen
• Mathematically guaranteed fairness
• 1:1 correspondence with no duplicates or omissions
• Visually transparent
• Applicable in various situations

And in modern times, online Amida-san enables remote participation and large group support.

Try Amida-san today and experience fair and transparent selection for yourself!