CS130 Software Tools. Fall 2010 Intro to SPSS and Data Handling

Transcription

1 Software Tools Intro to SPSS and Data Handling 1

2 Types of Analyses When doing data analysis, we are interested in two types of summaries: Statistical Summaries (e.g. descriptive, hypothesis testing) Visual Summaries (e.g. tables, graphs) Statistics is sometimes broken up into two different areas: Descriptive Statistics - a situation is described by the statistics by the collection, summarization, organization and presentation of data. Inferential Statistics - where inferences are made from samples of the population (e.g. smokers smoking a pack of cigarettes per day have a higher cholesterol). In this area we get into Hypothesis testing. In the Descriptive Statistics world, we are concerned about each of the data characteristics found in large sample populations 2

3 Descriptive Statistics PASW or SPSS provides an functions to do certain types of descriptive statistics like: Mean, Mode, Frequencies, and so on These are some of the most common statistics and are usually the simplest to understand Descriptive statistics are found under the Analyze menu item 3

4 Measures of Variables In SPSS, much difficulty for any student is around the setup of the variable and in particular an area called the Measure of a variable. It is often confused with the variable type, such as Numeric as the type and so Measure must be Nominal. Not true Has considerable impact of the quality and accuracy of the results and what you can graph To add to the confusion, different people call the variable measures different names 4

5 Measures of Variables 5

6 Another way to look at this The Measurement of a variable is basically assigning numbers to groups Lussier, 2002 Measurement is the assignment of number values to dependent or independent variables In Nominal, there are at least two scales to assign numbers, e.g. Political Party (1=Democrat, 2=Republican) There really isn t a ranking at all, the numbers just represent a grouping 6

7 Still More An ordinal variable is assigned numbers that can be ranked There is usually three or more values that have some meaning, e.g. quality of food (1=poor, 2=good, 3=excellent The number can be assigned any way that works for the user, the scale ordering does not have any significance 7

8 Tutorial For a more scenario-based learning experience, you can review the tutorials provided. There are also books in the library and available online I will list additional resources on our website as I find new items 8

9 Collecting Data While for small studies, you might be able to input you own data, in most cases, the number of cases of data required to be statistically relevant is far too great for manual data entry You will most likely be importing data from either a custom text file, e.g. comma separated variable (CSV) or Excel (XLS) To do this successfully, you still must know quite a bit about your source data 9

10 Importing Data from Excel You import data by opening a file of a known type SPSS support many of the most common file formats Excel SAS Text Lotus (wow, a throwback) 10

11 Importing Data from Excel You need to know how much data you have in the input file You should know if the names of variable are at the top of each column in the first row Like Excel, you can create multiple worksheets in SPSS, so you can name them for your own purposes 11

12 Importing Data from Excel If all goes well, you will end up with the same data in the proper form in SPSS By default, you will be in SPSS Data View One further step is required 12

13 Importing Data from Excel You must switch to Variable view And review each (yep, every one) variable and make sure all the attributes are correct Remember, SPSS doesn t know what you intend and the import is just a straight import 13

14 Performing Some Analyses Now that you have some data imported, you can look at it and start to understand it Use your knowledge of descriptive statistics to calculate the mean of any variable of your choice Investigate the output (results) window 14

15 In-class exercise 7 15