Recodes, dummy variables, and product terms can be generated temporarily within the program itself, so that the user will not have to create such variables before running a regression.
One numeric variable is specified as the dependent variable or the variable to be predicted. In order for this variable to be used as a dependent variable in logit or probit regression, it must be coded to have exactly two categories: 0 and 1. If the variable you want to use as a dependent variable is not already coded as a simple 0/1 variable, you can create a dummy variable, or you can recode the variable temporarily. If the dependent variable is left as anything other than a simple 0/1 variable, the program will recode the dependent variable automatically. The lowest valid score will be recoded to the value '0', and all other scores will be recoded to the value '1'.
Ordinarily this program is invoked by the Web interface for the SDA programs, and the user does not have to deal with the keywords given in this document. Output from the program is generally in HTML, which can be viewed with a Web browser.
It is also possible to run the program directly by preparing a command file, which specifies the variables to be analyzed and the options to use. This document explains how to prepare such a file. The name of this batch command file is specified to the program after the `-b' option flag.
Keyword Possible Specification Default (if no keyword) _____________________________________________________________________ COefficients= PROBIT Calculate LOGIT regression coefficients and results STUdy= path(s) of dataset(s) Look for variables in current directory only SAvefile= filename to receive output Output sent to screen (overwrites existing file) (standard output) DEP= name of dependent variable REQUIRED INDep= names of independent vars REQUIRED (separated by spaces/commas) Weight= name of weight variable No weighting Filter= name(s) and codes of filter No filter variable(s) STRatum= name of variable giving No stratification for sample stratum computing standard errors $1: Force one stratum CLuster= name of variable giving No cluster variable for sample cluster computing standard errors GVARCase= LOWER or UPPER No force to lower/upper case DUMMYgenmax= A number between 1 and 100 Max of 25 dummy vars can be (max dummy vars) generated by the "m:" syntax for a single categorical var NDEcimals= number of decimals for main 3 decimal places results (coefficients, SE's)
Keyword Possible Specification Default (if no keyword) _____________________________________________________________________ COLORcoding= Yes No color coding of coefficients or headings LAnguagefile= Name of file with non-English English labels on labels and messages output RUNtitle= Title or comments for run No title or comments SHORTlist= Yes (omit list of Output list of all indep vars at top) independent variables TExt= Yes No text for variables
You can specify the desired number of decimal places in parentheses for univariate statistics and 'BPRODuct' if the default, listed below, is not satisfactory. Note, however, that the number of decimals specified for 'BPRODuct' will override the number specified for 'UNIvariate'.
Keyword Possible Specification Default (if no keyword) _____________________________________________________________________ OTHERstats= TTests (ndec) No T-tests EXPB No exp(B) for logit FTest (ndec) No Global F-test UNIvariate (ndec) No univariate statistics BPRODuct (ndec) No B*Mean statistics COEFF (ndec) No covar of coefficients matrix CONF (90, 95, or 99) No confidence intervals ('CONF' alone gives 95% CI)
The statistic charted is each regression coefficient and its confidence interval.
Keyword Possible Specification Default (if no keyword) _____________________________________________________________________ TBLProperties= PATHNAME for chart properties REQUIRED for charts file Required location for SDA 4 is: SDAROOT/tmpdir/xxx.cht where 'SDAROOT' is the pathname of the SDA installation on your server, and where 'xxx' is any name. (See the last example below) (This is a temporary filename, to be passed on to the charting servlet.) CH_URL= URL of chart-generation REQUIRED for charts servlet on the server. Required URL for SDA 4 is: http://SDAURL/sdaweb/charts where 'SDAURL' is the hostname of the SDAWEB application on your server. (See the last example below) CH_COEFF= Coefficient to chart none (B or EXPB or PROBUNIT or PROBSD or NONE) CH_INDEPVARSmax=Number of independent vars all to include in the chart (first N variables, where N is an integer) CH_RANGEOPT= Set the range of the chart auto either to: AUTO (set by the program) or CUSTOM (use specified low/high) if CH_RANGEOPT=CUSTOM, the following two options can be used: CH_RANGELOW= Lower bound of the range (can have decimals) CH_RANGEHIGH= Upper bound of the range (can have decimals) CH_FONT= Font to use in the chart SansSerif CH_WIdth= Width of chart in pixels 600 CH_HEight= Height of chart in pixels 400
Keyword Possible Specification Default (if no keyword) _____________________________________________________________________ ASCiifile= Name of file for ascii output Only HTML output (for diagnostic purposes) MAXIter= Maximum number of iterations 15 NOVerbose= Yes Report results of each iteration in the ASCII output file (if 'ASCiifile=' is specified) TOLerance= Tolerance for convergence .0001
To change the number of decimals for the other (optional) statistics, put the desired number of decimals in parentheses after specifying the statistic. Note that requesting the BPRODUCT statistics will force the output of the univariate statistics as well. And the specification of decimal places for the BPRODUCT statistics will override any specification of decimal places for the univariate statistics.
This appending feature applies to the keywords for specifying the independent variables, the filter variables, and the 'otherstats=' keyword. It also applies to the 'study=' keyword, for specifying the locations of the SDA dataset directories. If other keywords are repeated, the program will print an error message and stop.
Specify the dependent variable as a dummy variable.
study = /sa/testdata dep = spend(d:1-2) indep = age, educ gender savefile = mylogit.htm
Redefine some ranges; use weight and filter variables; and request descriptive text for the variables.
dep = spend(d:1-2) indep = age(18-30) educ gender coefficients = probit otherstats = ttests otherstats = univariate weight= wtvar filters= var21(1-3) var30(1) text = yes savefile = mylogit.htm
dep = spend(d:1-2) indep = age, educ gender stratum = stratvar cluster = psuvar savefile = mylogit.htm
Also get 90% confidence intervals, and request some optional statistics, most with a specified number of decimals.
study = /sa/testdata study = /sa/testdata/newvars dep = spend(d:1-2) indep = age educ gender recodedvar otherstats = conf(90) otherstats = ttests ftest(4) coeff(8) bproduct(2) savefile = mylogit.htm
study = /sa/sdatest dep = vardep indep = spend1 spend2 spend3 spend4 age educ gender tblproperties = /var/www/sda/tmpdir/testing.cht ch_url=http://sda.berkeley.edu/sdaweb/charts ch_coeff = expb ch_indepvarsmax = 4 savefile = mymeans.htm