Created
November 6, 2014 18:04
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Item Characteristic Curve plotting with d3js.
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var N = 100, | |
a = 2.0, | |
b = 0.0, | |
c = 0.2; | |
var defaultScale = { mu: 0, sigma: 1 }, | |
enemScale = { mu: 500, sigma: 100 }; | |
// @return: The probability of hit at `theta`, or P(right | theta, a, b, c). | |
var prob = function (a, b, c, theta) { | |
return c + (1 - c) / (1 + Math.exp(- a * (theta - b))); | |
}; | |
var irt3p = function (theta) { | |
return prob(a, b, c, theta); | |
}; | |
var icc = []; | |
for (var i = 0; i < N; i++) { | |
// Change this to select the correct scale. | |
var scale = enemScale; | |
// The interval to be plotted is +- 3 standard deviations from the mean. | |
var theta = 3 * (i - (N/2.0)) / (N / 2.0); | |
icc.push({"theta": (theta * scale.sigma) + scale.mu, "prob": irt3p(theta)}); | |
} | |
// D3. | |
var margin = {top: 20, right: 20, bottom: 30, left: 50}, | |
width = 960 - margin.left - margin.right, | |
height = 500 - margin.top - margin.bottom; | |
var x = d3.scale.linear() | |
.range([0, width]); | |
var y = d3.scale.linear() | |
.range([height, 0]); | |
var xAxis = d3.svg.axis() | |
.scale(x) | |
.orient("bottom"); | |
var yAxis = d3.svg.axis() | |
.scale(y) | |
.orient("left"); | |
var svg = d3.select("body").append("svg") | |
.attr("width", width + margin.left + margin.right) | |
.attr("height", height + margin.top + margin.bottom) | |
.append("g") | |
.attr("transform", "translate(" + margin.left + "," + margin.top + ")"); | |
x.domain(d3.extent(icc, function(d) { return d.theta; })); | |
y.domain([0.0, 1.0]); | |
svg.append("g") | |
.attr("class", "x axis") | |
.attr("transform", "translate(0," + height + ")") | |
.call(xAxis) | |
.append("text") | |
.attr("x", width - 6) | |
.attr("dx", "0.71em") | |
.attr("dy", "-0.31em") | |
.style("text-anchor", "end") | |
.text("θ") | |
svg.append("g") | |
.attr("class", "y axis") | |
.call(yAxis) | |
.append("text") | |
.attr("transform", "rotate(-90)") | |
.attr("y", 6) | |
.attr("dy", "0.71em") | |
.style("text-anchor", "end") | |
.text("Probability of hit"); | |
svg.selectAll(".dot") | |
.data(icc) | |
.enter().append("circle") | |
.attr("class", "dot") | |
.attr("r", 1.0) | |
.attr("cx", function(d) { return x(d.theta); }) | |
.attr("cy", function(d) { return y(d.prob); }); |
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