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  • VIA Project
    These criteria are essential for the development of tests for measuring human performance In the following a summary of the three most important concepts shall be provided reliability validity and standardization Reliability refers to the consistency or repeatability of measures and relates to the quality of measurement If for example an IQ test yields a score of 90 for an individual today and 125 a week later it is not reliable Reliability can vary between 0 no reliability and 1 perfect reliability When applying a test for competency assessment purposes it is crucial to have a test featuring high reliability scores Acceptable tests usually have reliability coefficients between 0 7 and 0 9 For individual performance to be measured reliably reliability coefficients of at least 0 85 are recommended as minimum test statistics requirement Another important factor that has to be accounted for is test difficulty Especially if different tests are compared with each other it is important to pay attention to these attributes Two tests may feature similar reliability coefficients but completely different difficulty levels Validity indicates whether a test is able to measure what it was intended to measure Standardization involves administering the test to a representative sample of people in order to establish norms For more detailed information on these three important concepts in testing please refer to the chapter General Information How To Conduct Certification As mentioned above certification of screeners should contain a theoretical exam and an X ray image interpretation exam For the periodic certification practical exams can be conducted if considered necessary unlike the initial certification where it is required The exams should meet the requirements of high reliability and validity and standardization The theoretical and the practical exam are provided and carried out by the national airport authority X ray image interpretation exams can be obtained from www viaproject eu The theoretical exam should test the screener s knowledge of the regulations on aviation security screening Apart from national rules and specifications individual airports may enunciate questions covering special conditions This exam normally in the form of a questionnaire should be acceptably reliable It stands to reason to develop the exam as a multiple choice questionnaire Good questions with qualitatively high answer possibilities including distractor answers are the basis for a good questionnaire which differentiates between knowledgeable screeners and those who have limited knowledge The X ray image interpretation exam can be adapted to the location in which a screener is employed i e cabin baggage screening hold baggage screening or both A so far rather neglected operational domain which should receive more attention also regarding training and certification is cargo and staff screening Since not every threat object always constitutes a threat during the flight depending on where aboard the aircraft it is transported screeners should be certified according to their location The certification of cabin baggage screeners should be based on cabin baggage images which contain all kinds of threat objects that are prohibited from being carried on in cabin

    Original URL path: http://www.viaproject.eu/productsCert.php (2016-04-28)
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  • VIA Project
    is essential that a large library of threat objects is implemented in an individually adaptive training system Additionally it is not necessary that harmless objects are integrated into the training image library because screeners are confronted with harmless objects all the time during work Very important is not only that the image library is large it is also important that the threat objects are displayed from different viewpoints Additionally fictional threat items FTIs should be displayed on a new position in the bag each time to avoid that people learn the FTI bag combinations The image library used for training can of course be adapted to the work environment For example the image library for a training system for passenger bags control is different from staff bags control Of course for cabin baggage screening CBS another image library is used than for hold baggage screening HBS because for HBS IEDs are the most dangerous threat objects whereas missing a knife in a hold baggage is less dangerous But for CBS all four categories of threat items guns knives IEDs and other should be integrated into the training system The training library should therefore be optimally selected depending on the job requirements and must constantly being updated with new kinds of threat objects Feedback A very important aspect of training is that screeners get feedback after each image At least feedback should be given if a threat was missed or detected hit or if there was a false alarm harmless bag judged as NOT OK or a correct rejection harmless bag correctly judged as OK A more improved feedback shows which object was missed and how it looks like as an X ray image and under normal light conditions Only then a representation of that threat object is built in the brain and makes it possible to recognize it in the future Monitoring Training Progress Normally screeners can use the training system on their own without any supervision To make sure that screeners really train the training progress should be able to be monitored by training instructors or supervisors For example the amount of training hours the number of images that have been seen during training and finally the training progress e g difficulty levels are important indications about training progress For an overview about the usefulness of IEFs see Michel Koller Ruh and Schwaninger 2007 Training Duration Finally a training session should not be too long We recommend no more than three times 20 minutes per day at least 20 minutes training per week for an optimal training progress Very important is that screeners conduct recurrent training in order to keep screeners up to date regarding new threats and in order to maintain their x ray image interpretation competency How To Conduct Training During training the screeners task should then be to judge each bag if it is OK harmless bag or NOT OK containing a threat item Additionally to reduce guessing threat items can be identified by marking them

    Original URL path: http://www.viaproject.eu/productsTraining.php (2016-04-28)
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  • VIA Project
    screeners have acquired the competency to detect different threat items in X ray images of passenger bags should contain X ray images of bags with different categories of prohibited items according to an internationally accepted prohibited items list Standardization developing population norms The third important aspect for judging the quality of a test is standardization This involves administering the test to a representative group of people in order to establish norms normative group When an individual takes the test it can then be determined how far above or below the average her or his score is relative to the normative group It is important to know how the normative group was selected though For instance for the standardization of a test used to evaluate the detection performance of screeners a meaningful normative group of a large and representative sample of screeners at least 200 males and 200 females should be tested In summary competency assessment of X ray image interpretation needs to be based on tests that are reliable valid and standardized However it is also important to consider test difficulty particularly if results from different tests are compared to each other Although two tests can have similar properties in terms of reliability an easy test may not adequately assess the level of competency needed for the X ray screening job Signal Detection Theory d and A Figure 2 Seven ROC curves each of which correspond to a different d value 0 0 5 1 0 1 5 2 0 2 5 3 0 The higher the d value the higher the detection performance For example screener A has a detection performance of d 2 5 which represents a much better detection performance than screener B and C with d 0 5 A2 is the same screener as A but with a more liberal response bias The same is true for B2 and B Signal detection theory provides methods for calculating detection measures that are independent of subjective response biases and thereby provide valid indicators of threat detection performance This allows identifying screeners who can detect forbidden objects very well and at the same time are good in correctly identifying harmless bags The curves in Figure 2 are called receiver operating characteristics or simply ROC curves They represent a graphic description of how the hit rate of an observer changes as a function of changes in the false alarm rate Each ROC curve is related to a different detection performance which is indicated by the measure d or sensitivity This measure is calculated by the formula d z hit rate z false alarm rate and has to do with the distance of an ROC curve from the diagonal In the formula z denotes the z transformation i e the hit rate and the false alarm rate are converted into z scores standard deviation units For example Person B in Figure 2 has a high hit rate but also a high false alarm rate Consequently d z hit rate z false

    Original URL path: http://www.viaproject.eu/productsGenInfo.php (2016-04-28)
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