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Chapter 7 - Analysing the Data Part IV - Analysis of Variance Chapter 1 - Behavioural Science and research Chapter 2 - Research Design Chapter 3 - Collecting the Data Chapter 4 - Analysing the Data Part I - Descriptive Statistics Chapter 5 - Analysing the Data Part II - Inferential Statistics Chapter 6 - Analysing the Data Part III - Common Statistical Tests Sources of data Samples and populations Sampling methods Quantitative and qualitative approaches Questionnaire design Coding of data Readings and links


Chapter 3: Collecting the Data


Missing values

A common problem with research and particularly survey research, is that some people do not answer every question. Some psychological questionnaires have over 500 items (the MMPI) and quite often somebody will miss answering a question. Occasionally I have had people miss a whole page of questions. What do you do with such data? Do you throw it out or do you find a way to use what you have?

The general answer is to code the missing values in a particular way and then tell SPSS that any occurrences of that code are to be treated as missing values. I tend to use a "-1" because this usually stands out clearly from the other data and you can get a sense for how random or non-random the missing values are by glancing over a printout of the data base. Other authors will suggest a 9 or 99, as long as the code you use cannot be a real number. To code a particular number as missing you need to look under the Define Variables procedures and then under Type. The large data base for Assignment II has one missing value.




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