var ctx = document.querySelector("canvas").getContext("2d");
ctx.fillStyle = "red"; ctx.fillRect(399,0,2,110);  // draw bias target
ctx.fillStyle = "rgba(0,0,0,0.07)";

function getRndBias(min, max, bias, influence) {
    var rnd = Math.random() * (max - min) + min,   // random in range
        mix = Math.random() * influence;           // random mixer
    return rnd * (1 - mix) + bias * mix;           // mix full range and bias
}

// plot biased result
(function loop() {
  for(var i = 0; i < 5; i++) {  // just sub-frames (speedier plot)
    ctx.fillRect( getRndBias(0, 600, 400, 1.00),  4, 2, 50);
    ctx.fillRect( getRndBias(0, 600, 400, 0.75), 55, 2, 50);
    ctx.fillRect( Math.random() * 600          ,115, 2, 35);
  }
  requestAnimationFrame(loop);
})();

<canvas width=600></canvas>