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Thread: Changes to experiment affects data files

  1. #1
    Join Date
    Nov 2005
    Posts
    3,318

    Changes to experiment affects data files

    [edited from support email]
    I recently added a new questionnaire to a pre-existing media lab experiment and after running about 10 people discovered that the new data are not aligned the same way anymore in SPSS or Excel. I thought it would just save the new variables to the end and/or in alphabetical order and insert missing values for those who did the study without the added survey, but this was not the case. Is there any way to use the new cases? Or perhaps (in the future) find a way to add surveys to an existing experiment without having to delete the data file and starting over?

  2. #2
    Join Date
    Nov 2005
    Posts
    3,318
    Ok, first the necessary stuff on clearing data (from the guide):

    When you make changes to your experiment, you often change the structure of your data. This can cause confusion in your data because one subject's data are always appended to the last. Consequently, it is always a good idea to clear your data folder after making changes to your study. If the existing data are important, then back them up and merge them later with the new data. If they are not important (e.g., they are just test files) then you can click the Clear Data button when entering the subject and condition IDs. This will delete everything in your data folder resulting in a clean start. Note that some people get very nervous about having this button so accessible. If that's you, there is a way to disable it—on the Preferences menu, simply click Disable Clear Data. Note that as of v2006, MediaLab will attempt to send cleared data to the Windows Recycle Bin if the experiment is stored locally (i.e., as opposed to on a network drive).

    But with that said..

    Sometimes, you've already run sessions when you discover that changes in the experiment have caused misalignment of data. There is a way to deal with this.

    1. Make two copies of the data files.
    2. In one set, delete the new (misaligned) cases
    3. In the other set, delete the header and old cases so you have only new cases.
    4. Clear the main data folder and run a test session.
    5. Open the resulting fresh data file and copy and paste all your new cases into it--this should work because the new data file(s) will have the appropriate structure for the new data you have been collecting.

    This will give you two sets of data--one for the old structure and one for the new. You can then use SPSS or Excel to merge the two sets based on common variables. Let me know if you have any trouble with it or if that sounds way too complicated.

    -Blair

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