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Serial measurements

Command:Statistics
Next selectSerial measurements

Description

When serial measurements have been performed, e.g. in a glucose tolerance test, it is often useful to summarize the data on every subject into one or two summarizing measures, such as:

These summary measures can be obtained and analyzed statistically with the Serial measurements command. The program will create a graph for the observations, and perform an appropriate statistical test to evaluate whether the summary measure differs between the different subgroups.

How to enter the data in the spreadsheet

While for any other statistical procedure in MedCalc, the data of one case have to be entered on one single row of the spreadsheet, for serial measurements MedCalc requires the data for all cases to be entered in one single column (Value in the example). Other columns in the spreadsheet must contain:

In the example, case 1 belongs to group "malabsorption" and the value 0.08 was measured at time 0, value 5.70 at time 30 and 3.22 at time 45.

Data for serial measurements statistics

If you have your data organized in a different format, such as the data at different times in different columns, you can use the Stack columns tool to reorganize your data.

Required input

Dialog box for serial measurements statistics

Variable Y (data): this variable contains the serial measurements of all cases.

Variable X (time): this variable contains the time of the different measurements.

Case identification: a categorical variable containing case identification data.

Groups: a categorical variable containing group identification data.

Summary measure: here you select the summary measure of interest for statistical analysis

Options

Statistical analysis

For a parametric test, MedCalc uses the t-test when there are 2 groups, or One-way analysis of variance (ANOVA) when there are more than 2 groups.

For a non-parametric test, MedCalc uses the Mann-Whitney when there are 2 groups, or the Kruskal-Wallis test when there are more than 2 groups.

Test for Normal distribution: the option to select a test for Normal distribution is only available when you select "Automatic" statistical analysis.

Results

The results window displays the statistics (sample size, mean, SD, etc.) for the selected summary measure in the different subgroups. Next, a statistical test is performed to test the hypothesis that there is no difference between the subgroups. If the resulting P-value is less than 0.05, the conclusion is that there is a significant difference of the summary measure between the different subgroups.

Serial measurements statistics

Graph

The Serial measurements diagram plots the serial data consecutively, for every case.

Serial measurements statistics graph

If there are many cases, you may want to create different graphs for each subgroup. To create a serial measurements graph for all cases in the "normal" group, enter the following in the Filter box:

Select subgroup using a filter.

which gives the following graph:

Serial measurements statistics graph

For the "Malabsorption" group, you select:

Select subgroup using a filter.

which gives the following graph:

Serial measurements statistics graph

Literature

See also

External links