Effect Size Calculator for T-Test


How to derive standard deviation from standard error


SD=Standard error * sqrt(N);





QC: I checked the algorithm using SAS. The result was consistent with the algorithm (i.e., SD=standard error*sqrt(N)).

proc means data=sashelp.class mean std stderr n; var height; run;

ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ Mean 62.3368421

SD 5.1270752

Stadard Error 1.1762317

N 19 ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ

percentile quantile quartile



How to adjust weights so the sum of weights = n of subjects in the sample

This SAS code adjusts weights (e.g., sample weights) such that the sum of weights equals the sample size. Weight1 is the original weight and weight 2 is the result.

proc sql; create table comp2 as select *, psweight * (count(weight1)/Sum(psweight1)) as weight2 from comp;


The ASA's statement on p-values: context, process, and purpose


WWC effect size

What works Clearinghouse considers an effect size of .25 as “substantively important” and interpreted as “qualified positive” even when the effect size is not statistically significant.

See page 23.


Logistic regression result and odds ratio

Mathematically, you only need the coefficient for the predictor to derive an odds ratio (you don't need the intercept value).




Logic of model building


Tricky things to describe about stat model specification

When describing statistical models and results in writing, the following are tricky issues and require decisions and standardized way of description (and they must be brief, intuitive, full of meaning):

How do we choose omitted category/reference group? Why is there no level-1 error term in logistic regression? Why use HLM? Why use logistic regression model? […]

Cronbach's alpha

The UCLA site explains Cronbach's alpha as the average internal correlation among survey items. It also says that it is not a measure of unidimensionality. Rather, it is a measurement of internal consistency (though just intuitively I feel what is coherent tends to be also uni-dimensional… I think the point is that the measure is […]