Is there an easy way to merge multiple MediaLab data files?
Each subject's data are appended to the same constant data file for ease of analysis, so you won't have to merge any files that are collected on the same computer. You will however have to merge files collected on different computers. MediaLab offers a utility called FileMerge (located in the utilities folder) to do this rather painlessly. Essentially all you have to do is drag the files you want to merge into the FileMerge window and select "Merge Files" from the File menu. If you like, you can also save the list of files to merge them again later. A quick tutorial on FileMerge is available by clicking on the FileMerge Help menu. You can also start FileMerge by selecting Data > Merge Data Files from the main MediaLab menu.
How do I get SPSS to read the .txt data?
The easiest way to access your data in SPSS is to open the .sav data file located in the byVariablename data folder (see details above). However, if for any reason you want to import the raw text data files using SPSS syntax, here's how. If your experiment is called exper1, then the text file "exper1.txt" will have all your data in format that SPSS can read. The text file "exper1.sps" will be the input list for SPSS to read. Just open "exper1.sps" in SPSS and it will read the exper1.txt" file. It will automatically assign variable formats and variable names. You can start analyzing immediately. At the top of the .sps input file are a number of things to check for to make sure you don't get any errors (variable names over 8 characters and that sort of thing). Once the data has been read into SPSS, you can save it as a .sav file, analyze it immediately or export it into almost any other database format.
How do I get Excel to read the data?
If your experiment were called "exper1" then also written to the data folder will be a file called "exper1.csv". This file will have all your data in a format that Excel can read. Just open this file with Excel, and it will automatically read in the data, variable formats, and variable names. You can then save the file as an .xls file readable by almost any stats package. Be careful though, Excel can only read 255 variables. If you have more variables than that (including response times), then you may want to have SPSS read in your file.
How do I get SAS and other packages to read the data?
Most stats package will read the .csv file (this is the comma-delimited file in the data folder of your experiment directory. If not, have Excel read the .csv file and then have your stats package read the Excel file. Some will require you to save the Excel file in an earlier version (e.g., as an Excel 4.0 worksheet).
How do I determine the order in which random items were presented?
There is routine that keeps track of the actual presentation order of everything (e.g., of files and questionnaire items that are presented randomly).
At the end of the experiment you can find a log file called question_order.csv in the ByQuestionnaire data folder. The first row is the order of files (i.e., from the .exp file) and the remaining rows are the question orders for each questionnaire in the order they actually occurred. there is also a time stamp written to verify the time at which each questionnaire was started.
How can I tell exactly when an item was presented—i.e., in real time?
By entering @ in the parameter field for any item in a questionnaire, you can have MediaLab write a timestamp at the onset of the item. When you do this, a timestamp will be appended to a file called timestamps.csv in the data folder. It will include the subject id, the variable name, the time at which the item *started* (e.g., 12:23:22), the milliseconds elapsed from the beginning of the experiment and the milliseconds passed since the last timestamp.
Because large quantities of text do not play well with most data files, the responses of subjects to essay items will be written to their own separate data files located in the main data folder. The file will be named after the variable name you use for the essay. For example, if you have an essay item called ess1 then look for your essay data in a file called "ess1.txt" in the main data folder. The responses of all subject to this question will be appended there along with their subject and condition IDs.
Can I change the values written to the data file?
On scale responses and thought ratings, the default value written to the data file is always the ordinal value of the response option. For example, if the first option is chosen then a 1 is written to the data file—even if the button label read A, -5 or 0. For multiple response items, the default value of a chosen response is always 1, i.e., the option was either chosen or not. For all of these item types you can specify an alternate value for any given response option. This simply saves you from having to recode the data after collecting it. To specify an alternate value, specify it in squiggly brackets after the text label like so:
Note that the value can be text or numeric although numeric is recommended. If you use text, make sure the Write as Text option is checked for the item.
Can I change the value used for missing data?
By default, 99 is used as the value for missing data. Because most item types are either open ended or limited to a numeric value of 12, 99 is usually safe. However, if you suspect 99 might be a dangerous value for your particular study you can choose an alternate value. Simply create a text (.txt) file in your experiment folder and name it "missing.txt" and on the first line of that file, enter the alternate value. It must be numeric.
What is the Clear Data button for and can I disable it?
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).
How do I create a vertical format data file?
Occasionally, you may want to access your MediaLab data in a vertical format--i.e., one variable per row--rather than the usual horizontal format (all data for each subject located in a single row). Located in the folder C:\MediaLab\Utilities\Vertical Data is a file called vertical.mdb. This file is a blank Access database. This file can be copied into the "\data\byvariablename" subfolder of any experiment you like. If MediaLab finds this file after a session is complete, it will output all of the data into three columns (subject, varname, value) of the "vertical" table. MediaLab will always append data to whatever data already exist in the file and this function will be in addition to all of the usual data file formats. To maximize compatibility, this file is in Access 97 format--consequently it is readable by all versions of Access. A simple test of this function would be to copy the vertical.mdb file into the "c:\medialab\sample1\data\byvariablename" folder and run that sample--you should find the results stored in that file after you run the session. This is also a handy way to programmatically access data immediately after a session for use in other programs.
How to save data from a custom item made with HTML
See Custom Items
Can I use Long Variable Names?
As of MediaLab v2008, the limit for variable names was increased to 60 characters. Keep in mind though that some statistical packages and spreadsheet applications may still have difficulty working with longer variable names. Be sure to view and analyze some practice data before going too crazy with this feature!
See Also