Agile And Scrum Q15 - How do we estimate work in Scrum , and what are the common scales used ?Question For - Junior Level Developer

Question

Agile And Scrum Q15 – How do we estimate work in Scrum , and what are the common scales used ?Question For – Junior Level Developer

Brief Answer

In Scrum, work is estimated using story points, which are abstract units representing the relative effort, complexity, and uncertainty involved in completing a task. Unlike time-based estimates, story points acknowledge the inherent unpredictability of software development, fostering better team understanding and reducing pressure.

Common scales used for story point estimation include:

  • Fibonacci Sequence (e.g., 1, 2, 3, 5, 8, 13): This scale reflects increasing uncertainty for larger tasks, discouraging false precision.
  • T-shirt Sizes (XS, S, M, L, XL): A simpler, less granular scale often used for initial, high-level estimates.

The estimation process is typically collaborative, often using techniques like Planning Poker, where the team discusses and collectively assigns points. Over time, the team’s average completed story points per sprint, known as velocity, helps in forecasting and sprint planning.

Super Brief Answer

In Scrum, work is estimated using story points, which are abstract units representing the relative effort, complexity, and uncertainty of a task. Common scales include the Fibonacci sequence (e.g., 1, 2, 3, 5, 8) and T-shirt sizes (XS, S, M, L). This is typically done collaboratively using techniques like Planning Poker to aid in sprint planning and forecasting velocity.

Detailed Answer

In Scrum, teams estimate work using story points, which are abstract units representing the relative effort required to complete a task. Unlike traditional time-based estimates (like hours or days), story points account for the task’s complexity, uncertainty, and the amount of work involved, not just its duration. Common scales for assigning story points include the Fibonacci sequence (e.g., 1, 2, 3, 5, 8, 13) and T-shirt sizes (XS, S, M, L, XL). This approach helps teams embrace the inherent uncertainty in software development and plan more effectively.

What Are Story Points?

Story points are a core concept in Agile and Scrum for estimating the size of user stories or backlog items. They are a measure of:

  • Effort: The amount of work needed to complete the task.
  • Complexity: How intricate or difficult the task is.
  • Uncertainty: The level of unknowns or risks associated with the task.

Crucially, story points are about relative sizing. This means you compare the current task to previously completed tasks or to a baseline task. For instance, if a simple login feature is 3 story points, then a complex user profile management system that seems twice as hard might be 8 story points. The actual time it takes to complete an 8-point task will vary, but its relative size compared to the 3-point task remains consistent.

Why Use Relative Estimation (Story Points) Over Time Estimates?

While intuitive, precise time-based estimates for complex software development tasks are notoriously difficult and often inaccurate, especially early in a project. Agile embraces this uncertainty:

  • Embracing Uncertainty: Software development is often unpredictable. New technologies, unforeseen challenges, and changing requirements make accurate hourly predictions challenging. Relative estimation acknowledges this by focusing on comparative size rather than absolute duration.
  • Focus on Value, Not Hours: Story points shift the team’s focus from “how long will it take?” to “how big is it?” and “what value does it deliver?”. This encourages better prioritization and a focus on delivering incremental value.
  • Team Consensus & Shared Understanding: When a team estimates collectively using story points, it fosters deeper discussions about the task’s scope, dependencies, and potential challenges, leading to a shared understanding.
  • Reduced Pressure: Estimating in hours can create undue pressure on individual developers. Story points, being abstract, reduce this personal commitment to a specific time, allowing for more realistic planning.

It’s important to note that while story points are used for overall estimation and sprint planning, teams might still break down individual tasks within a sprint into smaller, hour-based sub-tasks for daily work management once they have a clearer understanding of the scope.

Common Scales Used for Story Point Estimation

To assign story points, teams typically use specific scales that provide granularity while acknowledging the increasing uncertainty for larger tasks:

1. Fibonacci Sequence

The most common scale is a modified Fibonacci sequence: 1, 2, 3, 5, 8, 13, 21, etc. The key characteristic here is the increasing gaps between numbers (e.g., 3 to 5 is a gap of 2, 8 to 13 is a gap of 5). This design is intentional:

  • It reflects the growing uncertainty as tasks become larger and more complex. It’s easier to differentiate between a 1-point and a 2-point task than between a 100-point and a 101-point task.
  • It discourages artificial precision for items with many unknowns. If a task feels “between 5 and 8,” the team is encouraged to discuss why and then settle on one, or break it down if it’s too large.

Some teams may extend the sequence with larger numbers (e.g., 20, 40, 100) for very large items, or use a “break it down” value (e.g., 100 or ‘infinity’) to signify that a task is too large to estimate and needs further decomposition.

2. T-shirt Sizes

Another popular scale uses T-shirt sizes: XS, S, M, L, XL, XXL. This scale is:

  • Simpler: It provides a less granular estimation, which can be beneficial for teams new to estimation or when high precision is not necessary.
  • Less Precise: The larger jumps between sizes inherently acknowledge uncertainty and encourage a high-level view of task size.

Teams might assign numeric values to these (e.g., XS=1, S=3, M=5, L=8, XL=13) to facilitate velocity tracking, but the conceptual simplicity remains.

The Estimation Process: Planning Poker

Planning Poker is a widely used, collaborative technique for estimating story points. It involves the entire Scrum team (developers, QA, product owner) and fosters rich discussions:

  1. The Product Owner presents a user story and clarifies any questions.
  2. Each team member privately selects a card representing their story point estimate (from a deck with Fibonacci numbers or T-shirt sizes).
  3. All team members reveal their cards simultaneously.
  4. If estimates differ significantly, team members with the highest and lowest estimates explain their reasoning.
  5. The team discusses the task further, addressing complexities, risks, or misunderstandings.
  6. The team re-estimates until a consensus or close agreement is reached.

This collaborative approach leads to more accurate estimates and a shared understanding of the work involved.

Understanding Velocity in Scrum

While story points estimate individual tasks, velocity helps predict a team’s capacity for future sprints and provides a basis for release forecasting.

Velocity is the average number of story points a team successfully completes and delivers in a single sprint.

Over time, as a team works through several sprints, their velocity tends to stabilize. Once a stable velocity is established, it becomes a powerful tool:

  • Sprint Planning: A team with a velocity of 40 story points knows they can realistically commit to approximately 40 story points in the next sprint.
  • Release Forecasting: If a larger feature or epic is estimated at 100 story points and the team’s velocity is 40, they can forecast it will likely take about 2.5 sprints to complete.
  • Stakeholder Communication: Velocity provides data-driven insights for product owners and stakeholders, enabling more reliable planning and expectation management.

It’s important that velocity remains a team metric and is not used to compare individual performance or pressure teams into artificial commitments.

Code Sample

Estimation in Scrum using story points is a conceptual and procedural aspect of Agile, and therefore, it does not involve a direct code sample. The concepts are applied through team discussions, planning tools, and collaborative techniques like Planning Poker.