choosing-trend-or-slope-view

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# Choosing a trend line vs a slope view

"How did X change between A and B?" is ambiguous. Two charts answer two different
questions, so **clarify before you build** unless the user already named one:

- **Change over time (line)** — the value at every interval across the range.
  Shows the _path_: dips, spikes, when it moved. This is the default trend.
- **Start vs end (slope)** — only the first and last point, one line per series
  connecting them. Shows the _net change_ and, across many series, which rose,
  which fell, and any rank flips — without the noise of the path between.

When the request could be either, ask a short either/or, e.g.:

> Do you want to see how it moved across the whole period (a line chart), or just
> the change from the start to the end (a slope chart)?

If the user clearly wants one — "just tell me how much it grew start to end" → slope;
"show me the trend / when did it spike" → line — skip the question and build it.

## How to render each

Both come from the **same** `TrendsQuery` over the same date range — the slope is
that series collapsed to its first and last point, not a different query.

### Change over time → line

Default trends behavior. Create or run a `TrendsQuery` and leave
`trendsFilter.display` as `ActionsLineGraph` (the default, "change over time"):

```json
{
  "kind": "TrendsQuery",
  "series": [{ "kind": "EventsNode", "event": "$pageview", "math": "total" }],
  "dateRange": { "date_from": "2025-01-01", "date_to": "2025-03-31" },
  "trendsFilter": { "display": "ActionsLineGraph" }
}
```

### Start vs end → slope

Run the trend with `posthog:query-trends`. The result card Max renders has a
**Line / Bar / Slope** view toggle — switch it to **Slope** to show each series as
a single line from its first to its last point, with the per-series change in the
legend. Tell the user they can flip to the Slope view on the result.

The slope view is best for a clean before→after comparison, especially with several
series/categories whose relative movement matters. Pick a date range whose two ends
are the points you want compared (the slope uses the first and last interval).

## Important limits

- **Two surfaces, one computation.** Both the inline slope (Max's `query-trends`
  result card) and the saved-insight slope (`ChartDisplayType.SlopeGraph`) show the
  same thing: the first interval's value vs the last interval's value, at the chosen
  group-by interval. The grouping defines the slope - group by month to compare the
  first vs last month, by day for the first vs last day. Use the inline view for a
  quick before-and-after on a result you're already looking at; use the saved display
  to persist it on a dashboard. A still-accumulating final period is shown as-is with
  a dashed connector, the same affordance the line chart uses for an incomplete tail.
- For period-over-period on a single series (this month vs last), a line with
  `compareFilter: { "compare": true }` overlays the two periods; a slope is the
  better fit when comparing the endpoints of **many** series at once.

From PostHog/skills, MIT.