Random Sampling and Creating Your Sample Data File
• Open the Table of Random Number.doc file on computer screen. The random sampling process works on this file and the completed file will be submitted as part of the assignment.
• Open the PopulationPropertyData.xls file on computer screen.
• Create a SamplePropertyData.xlsx Excel file and keep it open on computer screen throughout the whole process of completing the Task 1. Upon completion, this file is also be submitted as part of the assignment.
To select the sample data that form the basis of your assignment Part II and Part III, you will need to make use of the random number table provided as a MS word file (Table of Random Numbers.doc) on the Assessment Information page of the unit website. The table of random numbers is, as the title suggests, a sequence of randomly generated numerical digits (0 to 9). These digits are arranged in a table with ten columns (numbered 0 to 9) and one hundred rows (numbered 01 to 00) spread over two pages. The entries in each column of each row consist of six single digits. For example, the cell corresponding to Column 7 row 49 has a six-digit number of 613461.
Your first task is to select 50 three-digit random (property) numbers ranging from 001 to 400 from the table of random numbers. The type of simple random sampling that we will be engaged in here is termed “without replacement” because we specifically do not want to allow a property number to be selected more than once. If we allowed this to occur we would run the risk of the sample being biased and so not representative of the population.
In the population, a particular property only occurs once and so it would not do to allow a particular property to occur more than once in your sample. In this way we can be more assured that the sample is typical of the population and so perform inferential statistical analyses about the population with some confidence. The file is track changes protected which means that any changes by users will be shown up on the file so your lecturer will be able to monitor the progress of the random sample selection process and award marks accordingly.
In order to select your 50 random property numbers you will need to first go to a starting position row and column in the random number table (Note ~ not the population property data) defined by the last three digits of your VU student identification number. The last two digits of your VU ID number identifies the row and the third last digit identifies the column of your (relatively) “unique” starting position.
For demonstration purposes, if the last three digits of your student identification were 7, 4 and 9 (i.e. 749), you would commence your property number selection at the starting position - row 49 and column 7 of the random number table. You are required to colour/highlight the starting row number 49 and the starting column number 7 (refer to the Model Answer for Part I on VU Collaborate). You should be able to see that the six digit number occupying that position is 613461.
Then, moving across the row, from left to right from the starting position, examine the first three digits of each six digit number and then the second three digits in each of the columns of the table. If any of these three digit numbers are between 001 to 400 inclusive, they are “good” numbers (the population data numbered from 001 to 400). Ignore any number greater than 400 or equal to 000. Those numbers cannot be used in our sample selection process.
Continue reading across row 49 from left to right starting at column 7 as instructed, you would encounter the following three digit good numbers. You need to record the first good property numbers, i.e. 205, and go to the PopulationPropertyData.xls file located on the Assessment Information page of the unit website. On the spreadsheet, scroll down the PN column to locate 205 (note: do not select the Excel spreadsheet row number 205.
Please Select the row with 205 in the PN column). PN 205 refers to the two-hundred-and-fifth observation in the PopulationPorpertyData file. At this row, highlight from 205 under the PN column across to the right up to the V8 column, use Cut and Paste procedure to cut the row of data and paste the data into a new Excel file (name it and save it as SamplePropertyData.xlsx). Next is to repeat the Cut and Paste process for PN 184, and for PN 185 and the subsequent three digit good numbers selected from Random Number Table up to the point when the row of the spreadsheet in the SamplePropertyData.xlsx file grown up to 50 rows of data. Make sure you copy the column headings, PN, V1, ... V8 into your sample data file as the heading for the columns.
Each time a three-digit number is selected from the Random Number Table, yellow highlight the number to indicate that the number has been selected for the sample so your lecturer can award marks to the correct procedure. It is possible that you may come across some three digit good numbers more than once (we call them “repeated” numbers).
The use of the Cut and Paste procedure is the “without replacement” sampling procedure to ensure that no repeated PN number and the corresponding data can be select more than once in this sample selection process. When a repeated number is found, strikethrough the numbers to cross out the repeated number to indicate that this good number has not been selected as a sample observation (refer to the Assignment Part I Model Answers file for example).
That if you reach to the end of Row 50 on the first page of the Random Number Table but still not yet to collect 50 good numbers, continue the process on to Row 51 on the top of the second page of the Random Number Table (as the same practice in the Assignment Part I Model Answer). Similarly if you reach to the end of Row 00 on the second page, proceed on to row 01 on the top of the first page. Once 50 good numbers are selected and the 50 rows of data have been copied from the PopulationPropertyData file into the SamplePropertyData file, this will form a completed sample data set occupying spreadsheet Column A to Column I and spreadsheet Row 1 to Row 51 (Refer to the Assignment Part I Model Answers file on the Assessment Information).
The submission of Part I of the assignment simply requires the submission of two files online to the VU Collaborate Assignment Dropbox: the Table of Random Numbers.doc file and the SamePrppertyData.xlsx (both files must include student name and ID). The first file show your correct random sampling process and will be awarded for 5 points. The second file shows the correct sample selected from the PopulationPropertyData file based on the number selected from the first file. The correct second file will also be awarded for 5 points.
To prepare for the assignment, you are encouraged to consult reference/textbooks, seminar notes and having group discussions. However, your submission must be your own work on your own/unique data set. Be aware that the University penalties for plagiarism are severe.
