When creating health scores, it is often easiest and most accurate to include health factors using a linear range rather than a fixed increase or decrease.

Using a linear range ensures there's a proportional impact given to the factor within the specified range.

As a simple example, imagine you want to ensure you have contact with each of your customers every 15 days. You would likely use 'Last Touch' as your health factor and a linear range to reward more recent contact over less recent contact, resulting in something like this:

- There is a positive impact (+1 to 0) on the health score if we keep this number low: 1 to 6/7 days.
- A negative impact (0 to -1) if contact is towards the end of the range. 7+ days without an interaction with customers.

The Edge Case

A question that often arises is, what about results outside the range?

In the above example, if there has been no contact for 16 days, should this factor be ignored in the health score, or should 16 days be considered as the bottom of the range, therefore earning a -1.

In most scenarios the answer is "yes", you want results outside the edges of a linear score to be included in the health score. It would be illogical to say contact after 15 days was bad, but contact after 16 days was not, therefore this is the default in Planhat. We include results outside the boundaries meaning Linear scores visually look like this:

However, there are scenarios where this is not what you are looking for.

For example, you may decide that 5-10 tickets every 180 days is the right balance with your clients as it shows they are thoughtfully engaging with your product fairly frequently. Any more than that is negative because it means there is likely a problem, and less is also negative as it means you they are not engaged as much as you would like.

You therefore might use a linear scale for the specific range, but would need to balance it with negative values at the edges.

For example:

Tickets last 180:

Linear Scale: 1 - 3 points as Tickets last 180 go from 5 - 10.

With:

Tickets last 180:

Less than 5 tickets = -2 points

More than 10 tickets = -4 points

With this structure 4 Tickets in the last 180 days would create -1 points and 11 tickets would also create -1 points.

## Summary

In short, the Linear scale includes the edges and beyond.

If you are using one, you may want to balance the edges by including additional health factors! Easy peasy!