The University of Las Palmas de Gran Canaria (ULPGC) Harmful Algal observatory (OCHAB) recognises that regular quality control assessments are crucial to ensure a high quality output of phytoplankton abundance and composition data.  All our work is carried out in accordance to the standard requirements for PT schemes (ISO17043) and the data is statistically analysed using the statistical methods as laid out in ISO13528 ‘Statistical methods for use in PT by interlaboratory comparisons’. We use the statistical database software ProLab Plus from QuoData to do the statistical evaluation of the participants’ data.