Two computer programs to assist sampling calculations

In the course of obtaining information from a random sample, two stages can be distinguished. Before taking the sample, the main issues to be resolved are how to select the sample, how large it should be, and often how the total sample size should be allocated among groups of population elements. After taking the sample, the main tasks are to calculate point and interval estimates of the population characteristics of interest.

The program SampleCalc (short for Sample Calculator) is aimed exclusively at this second stage. It calculates unbiased point estimates and approximate confidence intervals of the principal population characteristics for each specified variable and each category of specified attributes under simple, stratified, two-stage, and cluster random sampling. It is assumed throughout that sampling is without replacement. The methodology is described in, among other sources, Peter Tryfos, Sampling for Applied Research: Text and Cases, Wiley, 1996, Chs. 3 to 5.

SampleCalc is a Microsoft Excel Add-In that can be loaded when needed and unloaded when not. Although the program SCALC  (included on the diskette accompanying the above text) can also be used for calculations after the sample is taken, the user must summarize beforehand the sample observations in the form of, say, group means, proportions, or variances for every variable and attribute of interest. By contrast, SampleCalc performs the appropriate preliminary calculations automatically on the sample observations. Also, because SampleCalc is an Excel Add-In, any corrections, changes, creation of new variables, and coding or re-coding of the sample observations can be carried by Excel just prior to the application of SampleCalc.

Instructions for the use of SampleCalc in Microsoft Word format (674KB) are contained in the file SCreadme.doc. A compressed version of the same file (304KB) is labeled The SampleCalc Add-In itself is the file SampleCalc.xla (308KB). The brief example used in the instructions is filed under Example1.xls (14KB). To download any of these files, right-click on their names, then follow your browser's instructions.

The program RCalc  is a Windows version of SCALC, the DOS program that accompanies Peter Tryfos, Sampling for Applied Research: Text and Cases, Wiley, 1996.  Like SCALC, RCalc is designed to assist and serve as a check of calculations  involving complicated formulas. Both programs are tied to the text---they are not independent products. 

In relation to SCALC, RCalc : (a) offers a graphical interface with menus and dialogs, making it easier for the user to know what information is required and to enter the required input; (b) provides a journal-like document where the input supplied and the results of calculations are stored, and which can subsequently be scrolled, printed or saved; and (c) includes some built-in Help. 

Instructions for installing the program can be found in the file rcalc.pdf (13KB). The main program file is rcalc.exe (285KB); it requires Windows 95 or NT or higher. The help file rcalc.hlp occupies about 1.7MB.

Please note that some text in dialog boxes of this program may appear partially obscured on certain monitors. This problem will be corrected in the next version  but does not hinder the functionality of the program.


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