Sample Size Calculator by wboykinm

index.html

<html>
<head>
  <title>Sample Size Calculator</title>
  <link href="//maxcdn.bootstrapcdn.com/bootswatch/3.3.0/paper/bootstrap.min.css" rel="stylesheet">
  <script src="confidence.js"></script>
</head>

<body>
	<script src="//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
	<script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.1/js/bootstrap.min.js"></script>
<div class="container">
    <h1>Sample Size Calculator</h1>

    <form id="calc" name="calc">
      <table class="table">
        <tr>
          <td>Confidence Level:</td>
          <td>
          	<label class="radio-inline"><input checked name="ConLevBut" onclick="ConLevButF1(this.form)" type="radio" value="1"> 95%</label>
          	<label class="radio-inline"><input name="ConLevBut" onclick="ConLevButF2(this.form)" type="radio" value="2"> 99%</label>
          </td>
        </tr>

        <tr>
          <td>Margin of Error:</td>
          <td><input name="box" type="text"></td>
        </tr>

        <tr>
          <td>Population:</td>
          <td><input name="popbox" onkeyup="this.value=iVal(this.value)" type=
          "text"></td>
        </tr>

        <tr>
          <td><input class="btn btn-primary" name="Calculate" onclick="to(this.form)" type="button" value="Calculate"></td>
          <td><input class="btn btn-default" name="Clear" onclick="cler(this.form,'')" type="button" value=" Clear "></td>
        </tr>

        <tr>
          <td>Sample size needed:</td>
          <td><input name="ssbox" type="text"></td>
        </tr>
      </table>
    </form>
  </div>
</body>
</html>

confidence.js

// Adapted from CRS: http://www.surveysystem.com/sscalc.htm

conInt = 0;
conLev=1;
zVal=1.96;
zValC=3.8416;
ss=0;
pop=0;
perc=0;
pf = 0;

function to(obj) {

  if (obj.box.value == "") {
    conInt=0
  }
  else {
    conInt = eval(obj.box.value)
  }

  if (obj.popbox.value == "") { 
     pop=0
   }
  else {
     pop = eval(obj.popbox.value)
  }

  if (conInt == 0) {
      alert("You must enter a confidence interval between .1 and 50.")
   }
  else {  
     if (pop == 0) {
        ss = ((zVal *zVal) * 0.25) / ((conInt / 100) *(conInt / 100))
     }
     else {
       ss = ((zVal *zVal) * 0.25) / ((conInt / 100) *(conInt / 100));
       ss=ss/(1+(ss-1)/pop)
     }
        
     obj.ssbox.value=parseInt(ss+.5)

  }
}

function ConLevButF1(obj){
   zVal=1.96
}
function ConLevButF2(obj){
   zVal=2.58
}
function ConLevButFC1(obj){
   zValC=3.8416 ;
}
function ConLevButFC2(obj){
   zValC=6.6564 ;
}
function cler(obj, string) {
  obj.box.value = string;
  obj.popbox.value = string;
  obj.ssbox.value = string;
}