Sampling consists of the following steps, each of which
will be described in detail:
- Selecting
the sampling technique to be executed:
- Random
- Numeric Stratified
- Categorical
Stratified
- Defining the
sampling parameters. For each of the sampling techniques, identify the
population size to be sampled and then use either of two available
modes to determine the optimal sample size:
-
Calculate Sample Size. Define
values for the factors in determining the sample size in a sample
calculator to automatically determine the recommended sample size.
-
Specify Sample Size. Enter
a fixed population or sample size to be used in the extract calculations.
- Executing
the report.
To confirm the number of records included in the sample
extract, you can run the procedure with the Message Viewer on. This
provides both the selected output and the messages confirming the
sample that was extracted. For information on how to turn the Message
Viewer on, see How to Set Message Viewer On.
x
Procedure: How to Extract a Sample Using Random Sampling
To
extract a sample using random sampling functionality:
-
Using Report Painter, add the fields to be included in the sample
extract to the Report Painter window.
-
Either select Sampling from the Report
menu or click the Options button on the output
format toolbar.
- If you choose Sampling from
the Report menu, the Report Options dialog box opens to the Sampling
tab.
- If you click
the Options button on the output format toolbar,
the Report Options dialog box opens to the Output tab and you need
to select the Sampling tab.
-
Select the Random radio button for the sampling
technique.
-
Identify the population size by clicking the Retrieve Population button
to retrieve the current total record count. The current record count
will be displayed on the retrieve button, as shown in the image
below. The sample size within the calculator will automatically
be updated with the recommended sample size for the population size
based on the defined margin of error, confidence level, and response
distribution.
-
Using the Population drop-down list, define which population
will be used to determine the sample size.
-
Live. Select Live from
the Population drop-down list to cause the total record count to
be recalculated at run time. Live is the default value.
-
Design-Time Count. When
you retrieve the population size during design time using the Retrieve
Population button, the value identified is added to the population
drop-down list. You can select this as your population size for
the run-time execution. Use this if you are certain the population
will not change between executions or if an estimate is sufficient
for your circumstances.
-
User-defined Count. Enter
any value for population by typing a numeric value into the Population
list box. Note that the Recommended Sample Size automatically updates
as you type new values for the population size, as shown in the
image below.
-
Define the seed value by using the default seed value or by
typing a new value into the Seed input box to be used to generate
the random sample.
-
Select how the sample size will be defined by selecting one
of the following options:
Calculate Sample Size
-
Click the Calculate Sample Size radio
button to activate the sample calculator.
-
Use the provided default values or type new values for:
- Margin of
Error (default value is 5).
- Confidence
Level (default value is 95).
- Response Distribution
(default value is 50).
The Recommended Sample Size will
be calculated and displayed, as shown in the image below.
Specify Sample Size
Click the Specify
Sample Size radio button to specify a user-defined sample
size.
- To specify
the sample size as a count, type a numeric value into the User Specified
Sample Size input box.
The Expected Margin of Error, based on
the identified Population size and your specified Sample size, will
be displayed, as shown in the image below.
- To specify
the sample size as a percent, click the As a percent check
box, and enter the User Specified Sample Size as a number between
1 and 100 to represent the percentage of the overall population to
be used as the sample.
The Expected Margin of Error based on the
identified Population size and your specified Sample size will be
displayed.
-
To execute the extraction with the defined random sampling,
close the Sampling dialog box by clicking OK and
run the report.
x
Procedure: How to Extract a Sample Using Numeric Stratified Sampling
To extract
a sample using numeric stratified sampling based on user-defined
ranges of a numeric field within the data:
-
Using Report Painter, add the fields to be included in the sample
extract to the Report Painter window. Be sure that the field you
will be using to define the strata is included in the report.
-
Either select Sampling from the Report
menu or click the Options button on the output
format toolbar.
- If you choose Sampling from
the Report menu, the Report Options dialog box opens to the Sampling
tab.
- If you click
the Options button on the output format toolbar,
the Report Options dialog box opens to the Output tab and you need
to select the Sampling tab.
-
Select the Numeric Stratified radio
button for the sampling technique, as shown in the image below.
-
From the list of available numeric fields in the current report,
select the field to be used to define the stratum criteria, as shown
in the following image.
Each
stratum or group is defined by the upper limit for the data value
of the current field. Strata are selected in the order they are
defined. Therefore, the criteria must be entered in ascending order.
In the example below, we will divide our population into four strata
based on the values for Profit.
Strata
|
Criteria Value Entered
|
Who Qualifies
|
Stratum 1
|
5000
|
-∞ Profit ≤ 5000
|
Stratum 2
|
10000
|
5000 < Profit ≤ 10000
|
Stratum 3
|
50000
|
10000 < Profit ≤ 50000
|
Stratum 4
|
999999
|
50000 < Profit ≤ 999999
|
Note:
- Numeric strata
criteria must be entered in ascending order to return the correct
results.
- Any data values
that fall outside of the defined criteria ranges will not be included in
the sample selection.
-
Use the strata toolbar to
manage your strata criteria.
- To add a new
stratum, either double-click in the next available criteria cell
or click the New icon.
- Enter each
criteria value. Press Enter to close the
current row and add the new criteria row.
- To remove
strata criteria, select the row to delete and click the X (delete) icon
on the toolbar or close the edit box for the strata criteria with
an empty value.
- To rearrange
the order of strata criteria, use the move item up and move item down
icons to arrange the strata criteria in ascending order.
-
Once your strata are defined, click the Retrieve Population button
to identify the record count and calculate the recommended sample
size for each defined stratum.
-
For each stratum, you can choose from the following options
to define the overall population from which to select your sample.
-
Live.
Select Live from the population drop-down list to cause the record
count to be recalculated at run time. Live is the default value.
-
Design-Time Count. When
you retrieve the population size during design time using the Retrieve
Population button, the value identified is added to the population
drop-down list. You can select this as your population size for
the run-time execution. Use this if you are certain the population
will not change between executions or if an estimate is sufficient
for your circumstances.
-
User-defined Count. Enter
any value for population by typing a numeric value into the Population
list box. Note that the Recommended Sample Size automatically updates
as you type new values for the population size.
-
Select how the sample size will be defined by selecting one
of the following options:
Calculate Sample Size
-
Click the Calculate Sample Size radio
button to activate the sample calculator. By default, the Calculate
Sample Size radio button is selected and the sample calculator is active.
-
Use the provided default values or type new values for:
The Recommended Sample Size will be calculated
and displayed, as shown in the image below.
Specify Sample Size
Click the Specify
Sample Size radio button.
By default, each of
the stratum sample sizes is set to the value of 1, which is the minimum
value allowed.
The
sample size can be specified as a count or as a percentage of each
stratum population.
- To specify
the sample size as a count, type a numeric value into the Sample
Size cell in the Strata grid for each stratum in your sample.
- To specify
the sample size as a percent, click the As a percent
of the population check box. Within the Stratum grid,
type a numeric value between 0 and 100 to represent the percentage
of the total records in the current stratum that should be included.
This number should represent the proportion of the individual stratum,
not the overall population.
Note: Click the Retrieve
Population button to refresh and calculate the Expected
Margin of Error based on the identified Population size and your
overall strata sample sizes.
-
To execute the extraction with the defined Numeric Stratified
Sampling, close the Sampling dialog box by clicking OK and
run the report.
x
Procedure: How to Extract a Sample Using Categorical Stratified Sampling
To extract
a sample using categorical stratified sampling based on alphanumeric
categories within the data:
-
Using Report Painter, add the fields to be included in the sample
extract to the Report Painter window. Be sure that the field you
will be using to define the stratum is included in the report.
-
Either select Sampling from the Report
menu or click the Options button on the output
format toolbar.
- If you choose Sampling from
the Report menu, the Report Options dialog box opens to the Sampling
tab.
- If you click
the Options button on the output format toolbar,
the Report Options dialog box opens to the Output tab and you need
to select the Sampling tab.
-
Select the Categorical Stratified radio
button for the sampling technique.
-
From the list of available fields in the current report, select
the field to be used to define the stratum criteria.
Note that all fields (character and numeric) that you selected
for your report are available within the Stratum Field drop-down
list.
The
image below shows that the Plant field was selected to be used to
define the stratum criteria.
-
Click the Get Data button to retrieve
the values of the field selected. This retrieves all available values
for your stratum field and makes them available for selection as
your stratum criteria.
-
Use the strata toolbar to
manage your strata criteria.
- To add a new
stratum, either double-click in the first criteria cell or click
the New icon and select a value from the
drop-down list.
- Enter each
criteria value or select the value from the drop-down list. Press Enter to
close the current row and add a new criteria row.
- To remove
strata criteria, select the row to delete and click the X (delete) icon
on the toolbar or close the edit box for the strata criteria with
an empty value.
- To rearrange
the order of strata criteria, use the move item up and move item down
icons to arrange the strata criteria.
-
Note: Any
data values that fall outside of the defined criteria will not be
included in the sample selection.
-
Click the Retrieve Population button
to identify the record count and calculate the Recommended Sample
Size for each defined stratum.
-
For each stratum, you can choose from the following options
to define the population to use to extract your sample.
-
Live. Select Live from
the population drop-down list to recalculate the record count at
run time. Live is the default value.
-
Design-Time Count. When
you retrieve the population size during design time using the Retrieve
Population button, the value identified is added to the population
drop-down list. You can select this as your population size for
the run-time execution. Use this if you are certain the population
will not change between executions or if an estimate is sufficient
for your circumstances.
-
User-defined Count. Enter
any value for population by typing a numeric value into the Population
list box. Note that the Recommended Sample Size automatically updates
as you type new values for the population size.
-
Select how the sample size will be defined by selecting one
of the following options:
Calculate Sample Size
-
Click the Calculate Sample Size radio
button to activate the sample calculator. By default, the Calculate
Sample Size radio button is selected and the sample calculator is
active.
-
Use the provided default values or type new values for:
The Recommended Sample Size will be calculated
and displayed, as shown in the image below.
Specify Sample Size
Select the Specify
Sample Size radio button.
By default, each of
the stratum sample sizes is set to the value of 1, which is the minimum
value allowed.
The
sample size can be specified as a count or as a percentage of the
overall population.
-
To execute the extraction with the defined Numeric Stratified
Sampling, close the Sampling dialog box by clicking OK and
run the report.
x
Procedure: How to Set Message Viewer On
To
confirm the number of records included in the sampled extract, you
can run the procedure with the Message Viewer on. This provides
both the selected output and the messages confirming the sample
that was extracted.
Select Message Viewer ON from the Run drop-down
menu, as shown in the image below.
This
provides both the selected output and the messages confirming the
sample that was extracted.
The image below shows the output
from the random sample defined in How to Extract a Sample Using Random Sampling.
x
Procedure: How to Disable Sampling
By
default, sampling is set to disabled. To select a sampling technique,
change the state of the Sampling radio button.
Important: To remove sampling
definitions that you have previously defined, change the Sampling
technique back to Disable Sampling. The current
sampling definitions are retained in the current procedure (fex),
until you save the procedure, but not used during report execution.
Once you save a procedure with sampling disabled, any previously
defined settings are removed.