The IAF MD 5: 2013, IAF Mandatory Document for Duration of QMS and EMS Audits, http://www.iaf.nu/upFiles/IAFMD52013QMSEMSAuditDurationPub.pdf
, in section 2.3 on Effective Number of Personnel, states the below:
The effective number of personnel is used as a basis for the calculation of audit duration. Dependent upon the hours worked, part time personnel numbers may be reduced and converted to an equivalent number of full time personnel.
Appropriate reduction should be made to the temporary unskilled personnel who may be employed in considerable numbers in some countries due to low level of technology and automation. Appropriate reduction of number of personnel also should be made where significant proportion of staff carry out a similar simple function for instance: transport, line work, assembly lines, etc.