Confidence intervals and other calculations

Spreadsheet confidence interval calculator
(makes comparisons between differing sample sizes and response distributions viewable at a glance)

Sample size calculator
(with confidence intervals-fromRaosoft)

Percentage calculator
(www.math.com/everyone/calculators/calc_source/percent.htm)

 

Graphpad's free statistical calculators

 

Sensitivity and Specificity
(link to Wikipedia) 

OpenEpi
(Open Source Epidemiologic Statistics for Public Health)

The Little Handbook of Statistics Textbook
(www.tufts.edu/~gdallal/LHSP.HTM)

HyperStat Online Statistics Textbook
(davidmlane.com/hyperstat/index.html)

 

Statistics Notes in the British Medical Journal
A series by Martin Bland and Doug Altman
(requires Athens login or similar)