It is too difficult to estimate effort in terms of time, so Scrum teams should focus on the following:
The source is important because it determines the clarity of the feature request. If the feature will meet a business need of a particular stakeholder, the stakeholder has analyzed and thought about what needs to be built. If a stakeholder is relaying a feature request, it will take more time to analyze and breakdown the feature into working software. The feature itself is more likely to evolve too.
Stability is the likelihood that the feature will change. Does the client know the business needs that need to be meant? Will the feature be changing during development? If any answer is no, then it will take more time to build the feature.
Complexity of the feature is based on several things: is the feature dependent on a third party? Does the feature replace an existing concept? Has the technology been used before? What must the sofware support? The higher the complexity, the more likely it will take more time.
The longer the team works on a project, the more knowledgeable the team will be in regards to technology, domain, and personalities. With time, the team will be able to provide more accurate Product Backlog estimates. When estimating Product Backlog, focus on effort rather than time. This will increase the accuracy of the team’s estimates.