Bar chart of mean plant height by fertiliser with error bars drawn from each low value to its high value, as given. fertiliser, mean (cm), low (cm), high (cm): none 12.4 11.3 13.5, A 15.8 14.4 17.2, B 17.2 16.0 18.4, C 14.9 13.3 16.5. y axis: height (cm).
Forma Visuals · Chart your data · Examples
Bar chart with error bars
Group means as bars, with error bars from the low and high values in the request, for a report or a poster.
For students and scientists · Vega-Lite
Try it in the consoleOpen the Vega-Lite editor
The playground allows illustrative values: any number your request does not give, Forma writes, and the answer says generated. Over the API and MCP, that request is refused unless it sets allow_generated_data.
01 The chart
Drawn from the code that came back.
valid · chart@cb3749b2 · 1 credit · 2026-10-07
Sent with the API's default setting, under which a chart is drawn only from values the request gives.
02 The request
In plain words, with its values.
03 What came back
A Vega-Lite spec.
Indented for reading.
{
"$schema": "https://vega.github.io/schema/vega-lite/v6.json",
"name": "plant_height",
"data": {
"values": [
{
"fertiliser": "none",
"mean": 12.4,
"low": 11.3,
"high": 13.5
},
{
"fertiliser": "A",
"mean": 15.8,
"low": 14.4,
"high": 17.2
},
{
"fertiliser": "B",
"mean": 17.2,
"low": 16,
"high": 18.4
},
{
"fertiliser": "C",
"mean": 14.9,
"low": 13.3,
"high": 16.5
}
]
},
"title": "Mean Plant Height by Fertiliser",
"layer": [
{
"mark": "bar",
"encoding": {
"x": {
"field": "fertiliser",
"type": "nominal",
"sort": null
},
"y": {
"field": "mean",
"type": "quantitative",
"axis": {
"title": "Height (cm)"
}
}
}
},
{
"mark": "rule",
"encoding": {
"x": {
"field": "fertiliser",
"type": "nominal",
"sort": null
},
"y": {
"field": "low",
"type": "quantitative"
},
"y2": {
"field": "high"
}
}
}
]
}04 When to use it
Where this chart helps.
- Comparing the means of a few groups, with the spread of each.
- The bars run from the low and high values you give. Work them out first, for example the mean plus and minus one SD.
- Say in the caption what the bars show, so the reader knows.