SPSS 202: Data Management by SPSS (Workshop) Dr. Daisy Dai Department of Medical Research 1

Log in SPSS CMH offers server version SPSS 18. Any employee can log in SPSS from your employee account. Go to Enter cmh user name and password. Click SPSS 18 icon. 2

SPSS Data Entry SPSS data can be entered manually. – The format is ready for analysis. SAS, Excel, txt, etc. data can be easily imported to SPSS. SPSS data files are saved as “SPSS data document (.sav)”. SPSS output files are saved as “SPSS viewer document (.spv)”. 3

SPSS Data Entry SPSS has a few unique features in data entry. – Categorical variables need to be coded. For instance, code male as 1 and female as 0 or vice versa. – When you have two treatments, test and control, please use 1 for test and 0 for control. – Categorical variables that are not coded in other sourced data files will not be imported or analyzed properly in SPSS. – Continuous variables don’t need coding. – Missing values needs to be defined in “variable view” page. 4

Example: CDC Survey Data An allergy survey was conducted in 2005 and 2006 to children more than 1 year old. Two data sets, allergy questionnaire and demographic information, are saved in sas export format. 5

CDC Survey Data 6

Tasks Import these two SAS data files (demo_d.xpt, agq_d.xpt) to SPSS and save them as SPSS data file. Sort each data set by study ID. Merge allergy variables and demographic variables. Save new data set as SPSS data file. 7

Task 1: Import Data We need to import two data sets to SPSS. – Allergy qustionaire: aqq_d.xpt (xpt is sas Xport Tranport File) – Demographic information: demo_d.xpt Please note that SPSS is on server and data must be saved in shared drive such as u drive or w drive. You will not be able to find the file in SPSS if you save them on your local disk. 8

Task 1: Import demo_d.xpt Click “File”, “Open”, “Data”. Select the folder where demo_d.xpt is saved. Choose “SAS (…)” for Files of Type. Select demo_d.xpt. Click “Open”. 9

Task 1: Import Data Select the folder. Choose agg_d file. Select xpt format. Click Open. Note: SPSS is compatible with other commonly used statistical and data management software packages. Excel, SAS, Access files are all convertible to SPSS. 10

Since this is not a SPSS data file, there is no file name (untitled) in the upper left corner. 11

Save demo_d f as SPSS data. Click “File”, “Save As”. File name: demo_d Save as type: SPSS7.0 (*sav). Click “Save”. 12

Missing Data In the data set, missing is in “.”, which is automatically treated missing. If missing data is in blank, then click “Missing”, “Discrete missing values” and enter a space. 13

Task 1: Import agq_d.xpt and save it as agq_d.sav(Exercise) 14

Task 2: Sort Data Variable to be sort: SEQN, that is, Respondent sequence number. 15

Task 2: Sort agq_d.sav Data Select aqd_d.sav data. Go to Data and select Sort Cases. On Sort Cases page, select the variable, Respondent sequence number. Click on right arrow. Choose Ascending or Descending. Click OK. 16

Practice Now let’s repeat this process by doing the following: – Open the demographic data, demo_d.xpt. – Sort the data by variable, Respondent Sequence Number. 17

Sort Variables “Sort variable” is different from “Sort Cases”. This function rearranges the columns of data. “Sort Case” rearranges the rows of data. 18

Task 3: Merge Two Data Sets Two data sets need to be linked by key variables. In our case, the key variable is SEQN- Respondent Sequence Number. Make sure the key variable has the same name and variable type in two data sets. Both data sets needs to be sorted by the key variable. 19

Task 3: Merge Two Data Sets Under demo_d.sav data set, go to Data -> Merge File -> Add Variables 20

Task 3: Merge Two Data Sets Choose “An open data set”. Click “agq_d.save” and “Continue”. 21

Merge two files 22

Split Files Very often, we like to perform separate analysis by groups (also called strata.) We can do so in SPSS by splitting files for groups. Task: In demo_d.save. Split the file by gender then get the mean of age for each gender group. 23

Split File Under demo_d.sav, click “Data”, “Split File”. Choose “Organize output by groups” Select “Gender” Choose “Sort the file by grouping variables”. Click “Ok”. 24

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Split Files Cancel the split file function when the task is done. Go to “Data”, “Split Files”. Check “Analyze all cases, do not create groups”. This is default. 26

Compute Variables Can be used to create new variables. Task 1: create a new variable age (month) for the existing variable age (year) Task 2: Log-transform age variable. 27

Compute Variables Under demo_d.xpt, go to “Transform”, “Compute Variable”. 28

Log transform variables 29