Read population
Read a new population file. Select the population from the list of available population files. Population files have the extension "pop".

Display variable
Display the population distribution of a variable in the population. Select a variable from the list of available variables.

Target variable
Select the variable for which the population mean must be estimated.

Sample design
Select the sampling design. This involves setting the sample size, and making a choice between sampling with equal or unequal probabilities. In case of sampling with unequal probabilities, an auxiliary variable must be selected. Elements will be selected with probabilities proportional to the values of this variabele. Only auxiliary variables assuming positive values can be used. Sample selection with unequal probabilities is only possible in combination with the direct estimator (i.e. the sample mean).

Estimator
Select the estimator. Four estimators are possible: the direct estimator (i.e. the sample mean), the ratio estimator, the regression estimator, and the post-stratification estimator. For the ratio, regression and post-stratification estimator, an auxiliary variable must be selected. These three estimators can only be used in combination with equal probability sampling. Note that for post-stratification, the auxiliary variable may assume at most 10 different values, and these values must be sequence numbers starting from 1. These sequence numbers indicate strata.

Generate nonresponse
To generate nonresponse, you must first select a nonresponse variable. The probability of nonresponse is taken to be linearly dependent on the values of this variable. You must specify the percentages of nonresponse corresponding to the highest and lowest values of this variable. For all values between these two bounds, the probabilty of nonresponse is obtained by means of intrapolation. Note that the entered percentages must be at least 1% and at most 99%.

Full response
You activate this option to switch off the nonresponse generating mechanism.

Parameters
You activate this option to specify the settings for the simulation process.

The first parameter that can be set, is the type of output. You can either produce a histogram of the sampling distribution of the estimator or 95%-confidence intervals.

The second parameter (Simulations) that can be set is the number of simulations. The default value is 1000, but you can set any number between 2 and 1000.

The third parameter (Scale) controls the horizontal scaling of the x-axis in the histogram of the distribution of the estimator. By setting a sample size, the lowerbound of the x-axis is taken to be the smallest value the estimator can assume for that sample size. Likewise, the upperbound is taken to be equal to maximum value of the estimator for this sample size. By increasing the value of this parameter, the lowerbound is increased and the lower bound decreased. It also possible to directly enter a lowerboud and upperbound of the x-axis.

The fourth parameter (Compression) controls the amount of vertical compression in the histogram. You can select a value from 1 to 4. A value of 1 means no compression. A value of 4 will compress the histogram by a factor 4.

Begin
After having set the simulation options, you start the simulation process by activating this option.

The vertical line indicates the population mean of the target variable to be estimated.

The simulation window contains a number of buttons:

By clicking on Next, the program will process the next sample of the simulation. This is the step-wise way of carrying out the simulation.

By clicking on Automatic, you switch to continuous simulation. All samples are processed one after the other without the possibility of interruption.

After the simulation has been completed, you press Statistics to get a numerical overview of the simulation results.

You can save the graph in a bitmap file by clicking on the Save button.

SimSam help
You cana ctivate this option to access the help system of SimSam.

About this program
You can activate this option to obtain more information about the program, like the version number and the developper.