IBM® SPSS® Amos™ 28
Fienberg (1977) presented the following frequency table from Wing (1962) obtained from 132 hospitalized schizophrenics.
|
STAY (Length of stay) |
|||
Low At least 2 years, but less than 10 years |
Medium At least 10 years, but less than 10 years |
High At least 20 years |
||
VISITING
|
Low Never visited and never goes home. |
9 |
18 |
16 |
Medium Visited less than once a month. Does not go home. |
6 |
11 |
10 |
|
High Goes home, or visited regularly. |
43 |
16 |
3 |
|
Part of the purpose of the study was to see if the length of a patient's hospital stay was related to how often the patient went home or was visited in the hospital. The frequency table shows that patients who were high on VISITING tended to be low on STAY.
The following figure shows one way that these ordered-categorical data might be entered into a data file. (Only 21 of the 132 cases are shown.)
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The file wing-a.sav |
Although we know that the categories go in the order low, medium, high, Amos will not be able to figure this out from the data file. In the case of the STAY variable, we have even more information that does not appear in the data file: We know that a measurement of low indicates a hospital stay that is between 2 and 10, a measurement of medium indicates a hospital stay that is between 10 and 20, and a measurement of high indicates a hospital stay that is greater than 20. All of this information can be placed in the data file by recoding the VISITING and STAY variables as follows. (This data file is saved as wing-b.sav.)
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The file wing-b.sav |
The recoding of the STAY variable is straightforward, although it may need explaining that no effort is made to distinguish between, say, "greater than 20" and "greater than or equal to 20". This is because numeric variables are assumed to have a continuous distribution with probability zero of being "equal to 20".
For VISITING, which has three categories and therefore two category boundaries, the two boundaries have arbitrarily been assigned the values 0 and 1. As explained in the topic, Choosing boundaries when there are more than three categories, the two boundaries can in fact be arbitrarily chosen.
Letting Amos do the recoding
Although Amos can read and interpret wing-b.sav, it is a chore to put a data file into that format. As an alternative, you can provide wing-a.sav as input to Amos, and then click Tools → Data Recode to open the Data Recode window. You can use the Data Recode window to specify that for the STAY variable, Low means "2 << 10", and so on.
