||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 SCreadme.zip. 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