We have started working with story points, and I am a bit confused by an (apparent?) contradiction, which shows up in most resources I have looked at so far.
On the one hand, the amount of story points should represent the relative effort required to complete a user story.
An item assigned a story point of two should take twice as much effort as an item assigned a story point of one. An item assigned a story point of three should take one and a half the amount of effort as an item assigned a story point of two.
On the other hand, the story points matrices I have come across implies a much faster increase in effort (see for instance https://i.stack.imgur.com/OK1sM.png ... from the same blog post as the quote above), so the story points are not "additive" at all.
At the moment, we are using the matrix in https://teamhood.com/agile/story-point-estimation-table but I don't feel confident to draw conclusions on velocity and sprint backlog sizing.
How are you dealing with this?
Story points do not represent efforts linearly, that's correct. That's why, we are using Fibonacci numbers to make this fact clear.
Besides, it is wrong to map story points with efforts. If story points are mapped to efforts, why we are using story points then? We can use efforts, directly, correct?
Story points are for relative representation of the complexity of the story. We look at stories and try to say "if story X is 3, then story Y is definitely 8!".