Item Characteristic Curve plotting with d3js.

icc.js

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); });