addumb.github.io/derp.html at master · addumb/addumb.github.io · GitHub

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---
sitemap: true
permalink: /derp.html
---
<!DOCTYPE html>
<html>
<head>
<title>Two sample z test between percents</title>
<script>
function gitit() {
    var p1 = parseFloat(document.forms[0].p1.value);
    var n1 = parseFloat(document.forms[0].n1.value);
    var p2 = parseFloat(document.forms[0].p2.value);
    var n2 = parseFloat(document.forms[0].n2.value);
    //z = (p1 - p2)/SD
    //SD = sqrt((p*(1-p)/n1) + (p*(1-p)/n2))
    p = (n1*p1 + n2*p2)/(n1+n2);
    SD = Math.sqrt((p*(1-p)/n1) + (p*(1-p)/n2));
    z = (p1 - p2)/SD;
    document.getElementById("z").innerHTML = z;
    P = doLeft(-z);
    document.getElementById("P").innerHTML = 2*P;
    if(P<0.001) {
        document.getElementById("significant").innerHTML = "Significant at ***";
    } else if (P<0.01) {
        document.getElementById("significant").innerHTML = "Significant at **";
    } else if (P<0.05) {
        document.getElementById("significant").innerHTML = "Significant at *";
    } else {
        document.getElementById("significant").innerHTML = "NOT significant";
    }
    return false;
}
function doLeft(z) {
    if(z<-6.5) return 0;
    if(z>6.5) return 1;

    factK=1;
    sum=0;
    itts=0;term=1;k=0;
    while(Math.abs(term)>Math.exp(-23)) {
        term=.3989422804*Math.pow(-1,k)*Math.pow(z,k)/(2*k+1)/Math.pow(2,k)*Math.pow(z,k+1)/factK;
        sum+=term;
        k++;
        factK*=k;

    }
    sum+=1/2;//alert(sum)
    if(sum<.0000000001) sum=0;

    return sum;
}
</script>
</head>
<body>
<h2>Two sample Z test for percentages or proportions</h2>
Hint: use the "0.8" form instead of "80" for the %
<form name="form" onsubmit="return gitit();">
p1: <input type="text" name="p1"/><br/>
n1: <input type="text" name="n1"/><br/>
p2: <input type="text" name="p2"/><br/>
n2: <input type="text" name="n2"/><br/>
<input type="submit" value="DO EET!"/><br/>
z is <span id="z"></span><br/>
P is <span id="P"></span><br/>
<span id="significant">Significance?</span>
</form>
</body>
</html>