Test towards reference

This section describes how the "Test towards reference" button works together with the "With condensed report" option. The behaviour is different depending on whether the reference is dated or undated. If you want the latter behaviour towards a dated reference, use the alternative button "(Test towards)...undated ref".

The Test Towards Reference command (button) can be used to check how well your collection members match towards a reference. This may be very suitable when you are building a new local collection and use a reference from a nearby area. You may even turn on the block checking mechanism to better see how each member matches.

Using Test Towards Reference when dating an unknown sample

The Test Towards Reference command can also be used to check how well a number of reference curves (stored within a collection) matches towards an unknown mean value sample which is then selected as being the reference in CDendro.
This is useful
either when you have no reference for the area from where your sample comes,
or when your sample is of unknown origin, e.g. from a wreck (a boat).

For this type of crossdating operation, you need a collection with all your usable references.

The collection above contains reference curves (=members) from several sites, some of them marked with red dots in the map below.
Each reference curve (=member) has been created from its own collection with the button command "Create mean value sample".
Then each such mean-value-sample has been saved in a .d12 file.
These normalized files have then been crossdated to each other and added to the dated collection shown above.

Note: Saving a mean value sample as a .wid file is not as useful as a .d12 file, as it is handy to have the .d12 files easily available with all their data (mean of ring widths, normalized values and standard deviations).
- On the other hand, mean value .wid-files can be saved within a single .rwl file which is also very handy.

For this excercise we will compare a mean value curve from Aneby in Småland with the curves of the collection above.

Sites with some shorter or longer reference curves are shown on the map.
Aneby is marked with a white dot.

Now, I have (not shown here) opened my Aneby collection and created a mean value sample out of it and also selected that sample as the reference.
In this case I already know that the Aneby collection should be dated to 2003, so it already has that dating information.
Before we click on the Test Towards Reference button we see to check the checkbox "With condensed report" under the Test Towards Reference button! This will extend the report with a condensed version suitable for a dating report.

Some comments:

When dating towards an undated reference the contents of the column groups in the report will be different.

To demonstrate this, I have created a 70 years long sample out of the Aneby mean-value-sample.
(Use the "Create sample from block-button" on the Curve display tab of the sample.)
Then I have selected that small sample as the reference and removed the dating information from it.
(Click the button "Set date of youngest ring" on the Workbench tab and erase the year.)

Now we have a somewhat undated short mean value sample from a site.
Let us see how the surrounding reference curves matches to that sample! - The result of "Test towards reference" is shown below.

Note: It is no longer necessary to make the reference undated! Use the "(Test towards)...undated ref" button to get the same report though the reference is still dated!

In this case the sum of all our references dates the "70 years long unknown reference-sample" to 2003.
Though members of the collection matches better at other years, mainly because of bad overlapping in time like the reference from Hurdal (Norway, only 22 years for overlap at correct match) and NMVK (Stockholm) which does not overlap at all at the correct position.

Now, for the sake of demonstration, let us think that 1916 was an interesting year.
How well do the other references actually match the 70 year Aneby data at the year 1916?
To check that, use the dating button "Set date of youngest ring" on the Workbench tab of the sample to make the sample "dated" to 1916!
(The button top on the Workbench will then switch to the text "Dated to 1916".)

The leftmost Corr-column of the uppermost table shows how all our reference curves "match" at the year 1916 - indeed with low values!

By first dating an unknown sample to a certain year, we can hereby get a table showing how well or bad several reference curves match the sample at that year!

Using "Select best matching members"

When your collection contains MANY members, some of them will have a LOW correlation to the "reference-sample" at their best matching point.
Then you want to uncheck those members which are not of interest for your comparisons.
Click the Select best matching members button to open a fixed selection "window".

If you are interested only in those members which have best match at year 2003, then fill in that number in the year-field and make the other fields empty.

If you also wanted to exclude (uncheck) members with too low correlation values at year 2003, then e.g. leave the correlation value at 0.40 and make the next two fields empty.

Then click Uncheck now!

If that resulted in too many unchecked members, click the "Check all" button on your form, adjust the values of the "Uncheck members..." window, and click "Uncheck now" again!

Then click "Clear report" button and then the Test towards reference button again to get a report with less members involved.

SummaryA mean value curve or an unknown sample is selected "as the reference" = Use the button "Select as reference".

Your dated collection contains members originating from old properly crossdated reference collections/reference curves.

When you click on the "Test towards reference" button you get a table showing how all these member files match towards the reference sample.

The column "Sets ref to" shows how all the different curves match (date) the sample curve to one or several years.

Note: The collection shown above has to be dated. Otherwise the "Sets ref to" column will not be shown.

Note: All reports are saved temporary in a .html file - Click the button "Open in NEW browser" to see the report.

Lars-Åke Larsson, Updated March 10 2011.