{
    "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
    "data": {
        "url": "https://vega.github.io/vega-lite/data/cars.json"
    },
    "description": "A scatterplot showing horsepower and miles per gallon for various cars with a global mean and standard deviation overlay.",
    "layer": [
        {
            "encoding": {
                "x": {
                    "field": "Horsepower",
                    "type": "quantitative"
                },
                "y": {
                    "field": "Miles_per_Gallon",
                    "type": "quantitative"
                }
            },
            "mark": "point"
        },
        {
            "layer": [
                {
                    "encoding": {
                        "y": {
                            "field": "mean_MPG",
                            "type": "quantitative"
                        }
                    },
                    "mark": "rule"
                },
                {
                    "encoding": {
                        "opacity": {
                            "value": 0.2
                        },
                        "y": {
                            "field": "lower",
                            "type": "quantitative"
                        },
                        "y2": {
                            "field": "upper"
                        }
                    },
                    "mark": "rect"
                }
            ],
            "transform": [
                {
                    "aggregate": [
                        {
                            "as": "mean_MPG",
                            "field": "Miles_per_Gallon",
                            "op": "mean"
                        },
                        {
                            "as": "dev_MPG",
                            "field": "Miles_per_Gallon",
                            "op": "stdev"
                        }
                    ],
                    "groupby": []
                },
                {
                    "as": "upper",
                    "calculate": "datum.mean_MPG+datum.dev_MPG"
                },
                {
                    "as": "lower",
                    "calculate": "datum.mean_MPG-datum.dev_MPG"
                }
            ]
        }
    ]
}