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File management

Data editing

Variables

Filters

Statistical procedures and graphs

Appendix A. Spreadsheet functions

File management

There are two ways to have your data on MedCalc.net. You can upload a data file, or you can just create a new empty file and enter the data on the website, but uploading a file in Excel or MedCalc format is the most convenient.

Click Files in the MedCalc.net menu.

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If you do not want to upload or enter any data at this point, the system has already created some files on your account, and you can start playing with the data in these files.

Upload file

To upload a file from your computer to MedCalc.net, click the Browse button and locate the file on your system. Next click the Upload button.

Whichever file format (Excel, CSV, etc.) you use, the data must be organized as follows:

  • Each column contains the data of one variable.
  • The top row contains the names of the variables. The top row should not contain numbers or other data.
  • The data for every case are entered on one row.
  • Do not code missing data with a number.

Note that the Upload file feature is not supported by all devices.

When you upload a file, the file is converted into a MedCalc.net specific format. Your file is not saved in its original format on MedCalc.net.

Create new file

Alternatively, you can start and create a new file on MedCalc.net by entering a file name and click Create.

Managing your files

If you do not longer need a file, you click the Delete file button to delete the corresponding file.

To download the file in Excel format to your computer you click the Excel format button.

Data editing

Click Data in the MedCalc.net menu to bring up the table data editor which shows the data of the active file. You can easily select a different file in the file selector above the data table.

The data are arranged in columns and rows. A column represents a variable and a row represents a case, sample or subject. All data for one case are entered on one row of the table. The top row contains the names of the variables.

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If you are working on a desktop PC, you can navigate in the table using the arrow keys, Page Up and Page Down keys, etc. Alternatively you can use the different buttons in the right side and bottom navigation bars, and the arrow buttons in the top toolbar.

To enter new data to the cell you move the cellpointer to that cell and enter the data. To start editing a cell you press function key F2 (if available) or click the Edit cell button.

Variables

Variables in MedCalc may be basic variables, which refer directly to columns in the data table or can be a combination of variables or a transformation of a variable.

The basic variable: column heading

These variables refer directly to columns in the spreadsheet.

  • The name of the variable is the heading you enter for the column in the spreadsheet
  • A variable name should not include any spaces, nor the following characters: - + / * = < > ^ ( ) $ " ' : ,
  • The variable name should not start with a number and it must be different from reserved words such as TRUE, FALSE, ROW and COLUMN
  • The variable name should not be equal to the address of a spreadsheet cell such as A1, S1, AB35, IL6, etc.

Combination of variables

A mathematical formula combining two or more variables. For example:

WEIGHT/(HEIGHT*HEIGHT)

Any of the following operators can be used to combine variables (in order of precedence):

^Exponentiation
-Negation
* /Multiplication, division
+ -Addition, subtraction

As shown in the example, brackets can be used to change the operators' precedence.

To create a new variable which is a combination of variables, see below: How to create a derived variable.

Transformation of a variable

When a variable needs transformation, you can use one of the many MedCalc spreadsheet functions. For example, if a variable needs square root transformation you use the SQRT(variable) function as a new variable.

To create a new variable which is a transformation of an existing variable, see below: How to create a derived variable.

How to create a derived variable

The example file ExampleFile2 contains data on body weight (in kg) and length (in m). You want to have a new variable Body Mass Index which is the weight divided by length squared.

Click Tools in the MedCalc.net menu. Next click Variables. The browser displays the variables in the data table.

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Click the New variable hyperlink. A new input panel is displayed which you complete as follows:

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Click Save and the new variable is added to the variables list:

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Filters

A filter is a logical expression which evaluates to 1 (= TRUE) or 0 (=FALSE). For every case in the data table, the expression is evaluated and if the result is TRUE, the case is included in the analysis or graph but if the result is not TRUE, then the case is excluded from the procedure.

Basic filter

A basic filter exist of a variable, a logical operator and a constant value. The relational operators, in order of precedence, are:

=Equality
<>Inequality
<Less than
>Greater than
<=Less than or equal to
>=Greater than or equal to

For example, if you have a variable AGE then the expression AGE>40 can be used as a filter.

Other examples of filters:

TREATMENT="A": Treatment must be equal to "A" - notice the use of quotation marks for text constant in formula.

AGE<=60: Age must be less than or equal to 60

ROW<21: Only the first 20 cases in the spreadsheet will be selected

Combined filters

Different filters can be combined into one single filter using the logical functions AND, OR and NOT, e.g.

AND(AGE>40,AGE<60): only cases with age more than 40 and less than 60 will be selected.

AND(AGE>40,TREATMENT="A"): only cases with age more than 40 and treatment "A".

OR(AGE>40,TREATMENT="A"): cases with age more than 40 or treatment "A" will be selected.

AND(AGE>40,OR(TREATMENT="A",TREATMENT="B")): cases with age more than 40 and treatments "A" or "B" will be selected.

When you have used a filter, you should check the resulting sample size and verify that the cases you intended to be selected have indeed been selected, and that you did not make a logical error in composing the selection filter.

How to create a filter

The example file ExampleFile2 contains data on body weight and length and included a variable Group. The Group variable contains the numbers 0 and 1 that identify two subgroups (controls and treated). You want to have a filter that select the cases belonging to group 0 and a filter that selects the cases belonging to group 1.

Click Tools in the MedCalc.net menu. Next click Filters. The browser displays the following (there are no filters defined yet for this data table):

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Click the New filter hyperlink. A new input panel is displayed which you complete as follows:

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Click Save and the new filter is added to the filters list:

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You proceed in a similar way for the second group, where group=1 for the treated cases.

Statistical procedures and graphs

Click Statistics in the MedCalc.net menu. You are presented with a menu of the statistical procedures available in MedCalc.net.

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For example, click Correlation. This will bring up the following input panel:

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You can select the data to be analyzed: the variables X and Y and optionally a filter. If any of the variables needs logarithmic transformation, you select the corresponding option.

In the example, an optional Scatter diagram has also been selected. Click OK and after some processing, the following results are displayed in the browser:

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This result section is followed by the scatter diagram:

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You can download the graph in PowerPoint format or as a high resolution TIF file by clicking the corresponding icon below the graph.