How to calculate
The calculations depend on the ability to break down every step of a task into the basic process level. The more detailed the analysis, the more accurate the model will be to predict human performance. The method for determining processes can be broken down into the following steps. * Write out main steps based on: a working prototype, simulation, step by step walk-through of all steps * Clearly identify the specific task and method to accomplish that task * For each final step identify sub-levels down to a basic process (in the diagram or chart below) * Convert into pseudo code (writing out methods for each step) * List all assumptions (will be helpful as multiple iterations are completed) * Determine time of each operation (based on the table below) * Determine if operation times should be adjusted (slower for elderly, disability, unfamiliarity, etc.) * Sum up execution times * Iterate as needed and check with prototyping if possible {, class="wikitable" , - ! Parameter ! Mean ! Range , - , Eye movement time , 230 ms , 70–700 ms , - , Decay half-life of visual image storage , 200 ms , 90–1000 ms , - , Visual Capacity , 17 letters , 7–17 letters , - , Decay half-life of auditory storage , 1500 ms , 90–3500 ms , - , Auditory Capacity , 5 letters , 4.4–6.2 letters , - , Perceptual processor cycle time , 100 ms , 50–200 ms , - , Cognitive processor cycle time , 70 ms , 25–170 ms , - , Motor processor cycle time , 70 ms , 30–100 ms , - , Effective working memory capacity , 7 chunks , 5–9 chunks , - , Pure working memory capacity , 3 chunks , 2.5–4.2 chunks , - , Decay half-life of working memory , 7 sec , 5–226 sec , - , Decay half-life of 1 chunk working memory , 73 sec , 73–226 sec , - , Decay half-life of 3 chunks working memory , 7 sec , 5–34 secPotential uses
Once complete, the calculations can then be used to determine the probability of a user remembering an item that may have been encountered in the process. The following formula can be used to find the probability: ''P = e''''-K*t'' where ''K'' is the decay constant for the respective memory in question (working or long term) and ''t'' is the amount of time elapsed (with units corresponding to that of ''K''). The probability could then be used to determine whether or not a user would be likely to recall an important piece of information they were presented with while doing an activity. It is important to deduce beforehand whether the user would be able to repeat the vital information throughout time ''t'', as this has a negative impact on the working memory if they cannot. For example, if a user is reading lines of text and is presented with an important phone number in that text, they may not be able to repeat the number if they have to continue to read. This would cause the user’s working memory’s decay time to be smaller, thus reducing their probability of recall.See also
*References
* Card, S.K; Moran, T. P; and Newell, A. ''The Model Human Processor: An Engineering Model of Human Performance.'' In K. R. Boff, L. Kaufman, & J. P. Thomas (Eds.), Handbook of Perception and Human Performance. Vol. 2: Cognitive Processes and Performance, 1986, pages 1–35. * Liu, Yili; Feyen, Robert; and Tsimhoni, Omer. ''Queueing Network-Model Human Processor(QN-MHP): A Computational Architecture for Multitask Performance in Human-Machine Systems.'' ACM Transactions on Computer-Human Interaction. Volume 13, Number 1, March 2006, pages 37-70. * Jastrzembski, Tiffany; and Charness, Neil. ''The Model Human Processor and the Older Adult: Parameter Estimation and Validation within a Mobile Phone Task.'' Journal of Experimental Psychology: Applied. Volume 13, Number 4, 2007, pages 224-248. ;Specific