Participation in an iis Proficiency Test allows a laboratory to compare its own performance to those of other, similar laboratories. The presence of systematic errors and/or random errors will be revealed, which allows the laboratory to take - if it feels necessary - corrective actions to improve its performance.

Furthermore, the results are compared to the requirements of internationally accepted analytical standard test methods (ISO, DIN, ASTM or other industrial standards). Each laboratory gets a performance score (z-score). Hopefully, this score - given by an independent institute - proves the laboratories good performance. Prove which can be used to convince your staff, your clients and you National Accreditation Body. See also other relevant information on this site: Proficiency Test and Statistics

Please fill in the form on the e-mail page and mail it us or send us a purchase order by mail or by fax. We will confirm your registration by fax and in due time you will receive the respective samples.

Yes. Since January 28, 2000, the iis quality system is in full agreement with ISO Guide 43 and ILAC G 13:2000. The accreditation was officially recognised by the Dutch Council voor Accreditation ('Raad voor Accreditatie', RvA). Our registration number is R007.

The VAT number of iis is NL004407726B02.

We will issue an invoice during the execution of the proficiency test. Invoices should be payed within 30 days after receipt.

We accept payment in Euros and in US Dollars. We prefer bank credit transfers.

See the 'Contact us' page for our bank details.

The Institute for Interlaboratory Studies is a small, but fully independent department of the SGS Group, world's largest organisation in the field of inspection, testing, analysis and certification.

As the results of our proficiency tests are used by accreditation bodies, we -as accredited organization- are not allowed to send a surplus of sample in order to avoid excessive testing to get good results. The sample amounts are sufficient to perform all tests once.

Our institute is accredited acc. to ISO Guide 43 en ILAC G13. In the accreditation documents is a requirement that tells us to use sample materials that are very realistic and like every day's routine samples. However as in practice hardly ever any forbidden components (e.g. AZO-dyes, metals or pesticides) are found in textile, this would mean that we should use samples without any contaminations at all. And that would not be suitable sample material in our opinion, because we cannot evaluate laboratory performance with only 'less than' results! Therefore we decided to use samples artificially contaminated with several components, and to use each round different components with different concentrations.  In this way the samples are like every day's routine samples for some components and at the same time give useful information for other components.

The participating laboratories do not have to perform all tests that are requested. Only tests that are performed routinely by the laboratory should be reported. And the laboratory may choose to perform only the tests that are most important for the laboratory. When the laboratory wants to have extra material for training purposes, the laboratory may request such material after closure of the deadline of reporting results. All remaining material is retained by iis and made available for the participating laboratories to be purchased. The amount of remaining material is limited and varies strongly per product. Please contact iis for more information.

Please report to us about the delay and test the samples as usual. We will evaluate all reported results, also when reported after the deadline for submitting results.

Contact us as soon as possible. We will send you new samples ASAP.

Participants are responsible for the customs clearance of the samples. For some countries the receiver needs to have an import licence. If you require us to attach documents to your parcel, we need to receive the documents at least two weeks before the sample dispatch date.

Yes. Although we have not a page on our web site to upload your results, we very much welcome all results that are sent to us by e-mail. In order to facilitate electronic reporting, all report forms are available in Word format on our website. See this download page to download the required form.

Yes, you can report results after deadline.

Of course we prefer that you will report results before deadline, but due to unforeseen circumstances it may happen that you are not able to report your results before deadline. Please be assured that we will evaluate your results always after receipt, also when we receive your results long after deadline. We will send you a special report (usually one page for one sample) with our findings.

Of course your results will not be published in the regular final report.

You should receive the report forms together with the samples. But occasionally the parcels are opened by customs and the forms do get lost. Therefore we also put the forms on our web site. See this download page to download the required form.

Results that re received by fax are not confirmed by us. However, when you report results by e-mail, we will always confirm receipt of your results.

Youden plots are meant for a two sample design, whereas iis organises proficiency tests using a single sample design.

The reason for this choice is our bad experiences with Youden plots. In some other interlaboratory studies the laboratories are asked to perform a duplicate analysis on one sample and the two results are considered a Youden pair, which is a wrong assumption. Furthermore the duplicates usually are contaminated with falsified results. The only reason for this falsification is a psychological one! Any sound thinking person will think twice before reporting bad duplicate results and will perform a re-test before reporting. So, in practice the reported duplicates are much better matching than the original duplicates. When the statistician subsequently uses a Cochran outlier test to delete all duplicates that do not fit in the data set, the only truly reported duplicate values will be seen as outliers and rejected! The same may occur when two samples are sent to the laboratories and both individual result are used as Youden pair. Even when the sample set consists of blind replicates. Perhaps it may work once, but after the first final report, the participating labs know that duplicate samples are used and will treat all subsequent samples as duplicates. The only way to avoid this problem is to send more than 2 samples (e.g. 3,4,5....) and let the results/concentrations/values differ only marginally. In this way the labs will not know which samples are duplicates and which are not. Youden plots can also be made for samples that are not replicates, but with values that differ slightly! But this last option will give the labs a lot of work (testing at least 3 samples for the same tests!).

So, there are some negative aspects to the use of Youden sample pairs. And as iis does not see many positive aspects (the only one we see is the determination of repeatability, but one does not need an interlaboratory study for that!), iis decided not to use Youden pairs and save the labs a lot of work by testing only one sample.

This way of z-score calculation results in a simple, straight forward comparison of lab results with the reproducibility stated in the corresponding international accepted test method. It indicates how many times the standard deviation the reported result deviates from the 'true value'. Target z-scores allow evaluation of performance over longer periods using a series of pt-results. This is impossible with z-score calculated from the standard deviation of the group of participants as the group of participants is not constant, nor is its performance. See also R.G.Visser, W.Oussoren, Accred Qual Assur 3:497-498.

In a proficiency test the performance of the participating laboratories is evaluated, while in a collaborative trial the performance characteristics of a Standard Test Method are determined.

Consequently in a proficiency test the laboratories use their usual test methods and the determination of a reliable assigned value is the ultimate goal, while in a collaborative trial only one test method is used - being the one under investigation - and the determination of the repeatability and the reproducibility is the ultimate goal.

Certificates of Excellence and certificates of Participation (see downloadable examples via this link: certificates) are available as of October 1, 2004. Only when all results reported by the laboratory are within the target reproducibility limits a certificate of Excellence may be issued.

The answer is simple: "NO!"

iis handles all information supplied by the participating laboratories with great care and strictly confidential. No information is passed to third parties unless prior permission is received.

The identity of individual participants is always maintained confidential and only known to a minimum of authorised iis-personnel. Furthermore, in all reports laboratories will only be represented by a code number.

The Institute is aware of the fact that participants of proficiency test do not always wish to enclose their performance to third parties. The identity of a laboratory can only be made public by the laboratory itself.

In order to assist the participating laboratories getting maximum efficiency from their PT-participation, Rob Visser - manager of iis - wrote some guidelines that were published in an article in the international journal 'Accreditation and Quality Assurance'.