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Using the ACBA Random Sampling Function
Background
The process of creating the sample takes place in two phases, but you will not always see the join. However there are always two closely related worksheets for each sample prepared. The data sheet lists and identifies uniquely all the pages of transaction trails and the numbers of transactions on each page. The sample sheet lists the randomly selected transactions in page and transaction number order.
The ACBA Function automatically gives them their own unique worksheet names. You can see these on the worksheet names tabs at the bottom of your screen. These names are in related pairs:
| DataSht00 | SampleSht00 |
| DataSht01 | SampleSht01 |
| DataSht02 | SampleSht02 |
DO NOT CHANGE THE WORKSHEET NAMES
Preparing the Data Sheet
The ACBA function assumes that the unique transaction identifiers are listed on paper (although it can be manipulated for use with electronic populations if required).
From the worksheet menu bar choose ACBA Functions, Random Sampling, Prepare Data + Sample. A dialog screen is presented which seeks the following information.
| Total sample size required | How many items do you want to test? |
| Test Name/Identifier | Words or a phrase that identifies the test you are performing |
| Source No. | This is entered by the ACBA function |
| Unique source name | The source of the population details (e.g. the financial year from which the transactions were taken) |
| No. of Pages in the Source | Any whole number greater than zero. |
| No. of Transactions on 1st Page | Any whole number greater than zero. |
| No. of Transactions on Inner Pages | Any positive whole number; must be zero if ‘No. of Pages in Source’ is 1 or 2. |
| No. of Transactions on Last Page. | Must be zero if ‘No. of Pages in Source’ is 1. |
All fields must be completed with valid entries. Click ‘Enter Details’.
The ACBA function immediately posts the information relating to this data source to the data sheet and the asks the question about a new data source:
"Do you want to continue with another sample list?"
In principle you may want several sources of data covered within the sample (e.g. transactions from the current year, last year and the year before). Clicking "Yes" allows you to enter these details into the transaction list. All the fields below the black dividing line must be entered. The system requires that the name of the source is different from all previous names.
Clicking "No" takes you on to the next phase. Before going on, however, you are asked:
"Do you want to proceed to sample preparation?
Click ‘No’ if you need to amend the numbers of transactions on some of the inner pages within your data list."
The ACBA function assumes that all inner pages have the same number of transactions listed on them. This may not always be the case. You have the opportunity here to amend the data list so that it reflects the transaction numbers listed on individual pages.
Preparing a Sample
The ACBA function will automatically select a random sample from your population as specified. This selection will not include any duplicates. It is presented to you on the ‘SampleSht**’ in batch reference, page number and transaction number order for ease of reference and testing.
Prepare a New Sample on Existing Population Data
Choose ACBA Functions, Random Sampling, Prepare New Sample. The dialog box drop down field lists all the sample sheets available according to the name or identifier you have given then during data preparation. Select the name or identifier that represents the population you want to retest, enter the sample size and click "Prepare Sample".
The ACBA function prepares a new random list of transactions in order next to the original list. The selection will not contain any duplicates, but is based on the whole data population. Previously selected items will not be excluded.
