<?php
function compute()
{
$roundunit=3;
$Tmean = $_POST['Tmean'];
$Cmean = $_POST['Cmean'];
$TSD = $_POST['TSD'];
$CSD = $_POST['CSD'];
$TN = $_POST['TN'];
$CN = $_POST['CN'];
$mean_dif=$Tmean-$Cmean;
$SE=sqrt(
(($TSD*$TSD) / $TN)+(($CSD*$CSD) / $CN)
);
$T=$mean_dif/$SE;
$DF=$TN+$CN-2;
$P="Under Development (Still working on this)";
/*I will get T for binary variable comparison*/
$N_SUCCESS_T=$TN*$Tmean;
$N_SUCCESS_C=$CN*$Cmean;
$P_=($N_SUCCESS_T+$N_SUCCESS_C)/($TN+$CN);
$Z_numerator=$Tmean-$Cmean-0;
$Z_denom=SQRT(($P_*(1-$P_))*((1/$TN)+(1/$CN)));
$Z_bin=abs($Z_numerator/$Z_denom);
$Z_bin_abs=abs($Z_numerator/$Z_denom);
/*$P=stats_dens_normal($T, 0,1);*/
/*$P=stats_dens_gamma(float $X, float $shape, float $scale);*/
/*$P= $T / 100 ;*/
/*Hedges g*/
/*g numerator*/
$g_numerator=($Tmean-$Cmean)*(1-3/((4*($TN+$CN))-9));
/*g demnominator*/
$g_denominator=SQRT(((($TN-1)* ($TSD**2) )+(($CN-1)* ($CSD**2) ))/($TN+$CN-2));
$hedges_d=$g_numerator/$g_denominator;
$hedges_d_abs=abs($hedges_d);
/*if binary variabels*/
$T_Odds=$Tmean/(1-$Tmean);
$C_Odds=$Cmean/(1-$Cmean);
$Odds_ratio=$T_Odds/$C_Odds;
$Tstep1=log($T_Odds);
$Cstep1=log($C_Odds);
$step2=$Tstep1-$Cstep1;
$WWC_binary_effect=$step2/1.65;
/*
if ($hedges_d >= 0.2) echo "Small Effect (Cohen)";
if ($hedges_d >= 0.5) echo "Medium Effect (Cohen)";
if ($hedges_d >= 0.8) echo "Large Effect (Cohen)";
*/
echo "<br>";
echo "WWC group comparison of continuous and binary variables";
echo "<br>";
echo "<br>";
echo "Treatment N:" .$TN;
echo "<br>";
echo "Treatment mean:" .$Tmean;
echo "<br>";
echo "Treatment SD:" .$TSD;
echo "<br>";
echo "<br>";
echo "Comparison N:" .$CN;
echo "<br>";
echo "Comparison mean:" .$Cmean;
echo "<br>";
echo "Comparison SD:" .$CSD;
echo "<br>";
echo "The group mean difference:".round($mean_dif,$roundunit);
echo "<br>";
echo "<br>";
echo "[RESULTS FOR CONTINUOUS OUTCOME]";
echo "<br><br>";
/*echo "Probability " .round($P,2);*/
echo "Probability: " .$P;
echo "<br>";
$abs_T=abs($T);
echo "T-score is: " .round($T,$roundunit);
echo "<br>";
if($abs_T < 1.96 ) {
echo "Not significant at alpha 0.05 (two tail test;I used a z-test and ignored degree of freedom; threshold 1.96)";
}elseif($abs_T >=1.96){
echo "Significant at alpha 0.05 (two tail test;I used a z-test and ignored degree freedom; threshold 1.96)";
}
echo "<br>";
echo "<br>";
echo "T-test (the same test as above but with three thresholds)";
echo "T 1.96, 2.576, 3.291, each for p=0.05, 0.01, 0.001";
echo "<br>";
if($abs_T < 1.96) {
echo "Not sig. at alpha 0.05";
}elseif($abs_T>=1.960 and $abs_T < 2.576 ){
echo "Sig at p=.05*";
}elseif($abs_T>=2.576 and $abs_T < 3.291 ){
echo "Sig at p=.01**";
}elseif($abs_T>=3.291 ){
echo "Sig at p=.001***";
}else {
echo "N/A";
}
echo "<br>";
echo "<br>";
echo "Hedges d " .round($hedges_d,$roundunit);
echo "<br>";
/*cohen's rule of thumb*/
echo "Cohen's rule of thumb for effect size interpretation";
echo "<br>";
if($hedges_d_abs < 0.2) {
echo "Close to zero and Not even small Effect (Cohen)";
}elseif($hedges_d_abs>=0.2 and $hedges_d_abs < 0.5){
echo "Small effect (Cohen)";
}elseif($hedges_d_abs>=0.5 and $hedges_d_abs < 0.8){
echo "Medium effect (Cohen)";
}elseif($hedges_d_abs>=0.8){
echo "Large effect (Cohen)";
}else {
echo "others";
}
echo "<br>";
echo "Baseline equivalence test";
echo "<br>";
if($hedges_d_abs <= 0.05) {
echo "Satisfies the baseline equivalence requirement";
}elseif($hedges_d_abs>0.05 and $hedges_d_abs <= 0.25){
echo "Requires statistical adjustment to satisfy the baseline equivalence requirement";
}elseif($hedges_d_abs>0.25){
echo "Does not satisfy the baseline equivalence requirement";
}elseif($hedges_d_abs>=10){
echo "Something Strange happened";
}else {
echo "N/A";
}
echo "<br>";
echo "<br>";
echo "[RESULTS FOR BINARY OUTCOME]";
echo "<br>";
echo "If outcomes were binary variables (range 0 to 1), the WWC effect size would be ";
echo "" .round($WWC_binary_effect,$roundunit);
echo "<br>";
echo "T-score for the binary outcome is: " .round($Z_bin,$roundunit);
echo "<br>";
echo "<br>";
echo "T-test for binary outcomes";
echo "<br>";
if($Z_bin_abs < 1.96) {
echo "Not sig. at alpha 0.05";
}elseif($Z_bin_abs>=1.960 and $Z_bin_abs < 2.576 ){
echo "Sig at p=.05*";
}elseif($Z_bin_abs>=2.576 and $Z_bin_abs < 3.291 ){
echo "Sig at p=.01**";
}elseif($Z_bin_abs>=3.291 ){
echo "Sig at p=.001***";
}else {
echo "N/A";
}
echo "<br>";
echo "<br>";
}
/*echo "The result is: " . compute();*/
compute();
?>
<br>
REFERENCE
<br>
Cohen's rule of thumb about effect sizes:
<br>
<li>If greater than 02, Small Effect
<br>
<li>If greater than 0.5, Medium Effect
<br>
<li>If greater 0.8 then Large Effect
<br>
Cohen, J. Statistical power for the behavioral sciences (2nd ed.). Hillsdale, NJ: Erlbaum (1988).
<br>
<a href="https://wmich.edu/sites/default/files/attachments/u58/2015/Effect_Size_Substantive_Interpretation_Guidelines.pdf">
Effect Size Substantive Interpretation Guidelines: Issues in the Interpretation of Effect Sizes Jeff Valentine and Harris Cooper, Duke University(see page. 5)</a>
<br>
<br>
WWC related info:
<br>
<a href="https://ies.ed.gov/ncee/wwc/Docs/ReferenceResources/wwc_procedures_handbook_v4_draft.pdf">WWC procedures handbook (see page. 14)</a>
<br>
<a href="https://ies.ed.gov/ncee/wwc/Docs/OnlineTraining/wwc_training_m3.pdf">WWC standards slides (Definition of small sample size correction, slide 14)</a>
<br>
WWC considers the effect size greater than .25 substnatively important.
<a href="https://ies.ed.gov/ncee/wwc/Docs/referenceresources/wwc_procedures_handbook_v4.pdf">P.22 of WWC standards</a>
<br>
T-Table
<br>
<a href="https://www.sjsu.edu/faculty/gerstman/StatPrimer/t-table.pdf">T-Table</a>
<br>
<a href="calc_t_test1.php">Back to the calculcator </a>
<br>
<a href="https://www.estat.us">My website</a>
<br>
<br>
