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Title / Evaluate sampling methods used within the New Zealand dairy industry
Level / 4 / Credits / 6
Purpose / People credited with this unit standard are be able to: explain the use of random sampling and factors which limit its practical use; calculate the mean and standard deviation and the proportion of data likely to lie within 1, 2 standard deviations of the mean; identify the difference between attribute and variable sampling, and use an attribute sampling plan; define sampling vocabulary and terms used in Codex sampling procedures; identify methods used in the New Zealand dairy industry to reduce the cost of true random sampling; plot data on Control and Cumalative Sum (CUSUM) charts; estimate the chance of rejection of a lot using an Operating Characteristic curve (OC curve); and determine the number of samples needed for problem solving investigations where a single defect in the sample denotes a problem.
Classification / Dairy Manufacturing > Dairy Laboratory Methodology
Available grade / Achieved
Explanatory notes
1Reference documents
Codex General Guidelines on Sampling (codex alimentarius commission FAO/WHO of the United Nations, CAC/GL 50, 2004) available from
2Definitions
Organisational Requirements refers to instructions to staff on policy and procedures which are documented in memo or manual format and are available in the workplace. These requirements include but are not limited to – site specific requirements, company quality management requirements, approved codes of practice and guidelines, and legislative requirements.
Legislative requirements in this unit standard refer to legislation and regulations that include but are not limited to – Animal Products Act 1999, Animal Products (Dairy) Regulations 2005, relevant Dairy Specifications/Notices.
3Data for calculations will be provided by the assessor.
Outcomes and evidence requirements
Outcome 1
Explain the use of random sampling and factors which limit its practical use.
Evidence requirements
1.1Random sampling is defined according to Codex General Guidelines on Sampling.
1.2Explanation identifies the two main reasons why random sampling is favoured.
Rangeinternational respectability, fairness (unbiased estimates of population parameters).
1.3Two situations in the dairy industry are identified, and reasons are given, in which true random sampling may be impracticable.
1.4A situation in the dairy industry is identified in which a sampling method apparently equivalent to the random sampling method may give a false result, and an explanation is provided as to the source of bias in the method.
1.5A random sample is produced from a defined population with an explanation of the method used.
Outcome 2
Calculate the mean and standard deviation and the proportion of data likely to lie within 1-2 standard deviations of the mean.
Evidence requirements
2.1The mean and standard deviation (n-1) are calculated from a given set of positive data.
2.2The proportions of data likely to lie within the limits of 1 standard deviation from the mean, and 2 standard deviations from the mean, are stated for normal distribution.
Rangea normal distribution with mean at least three times the standard deviation.
Outcome 3
Identify the difference between attribute and variable sampling, and use an attribute sampling plan.
Evidence requirements
3.1A given set of data is identified as containing variable or attribute data.
3.2A given set of E. coli results is identified as containing variable or attribute data.
Range19 out of 20 E. coli results are given as negative.
3.3A sample lot is determined as acceptable or rejectable from a given attribute sampling plan, sample size, acceptable quality level (AQL) of plan, and number of defectives.
3.4A given set of data is assigned a quality grade in accordance with the product specification.
3.5The producer’s risk is stated for a given consumer’s risk.
Outcome 4
Define sampling vocabulary and terms used in Codex sampling procedures.
Evidence requirements
4.1Sampling vocabulary and terms are defined in accordance with Codex General Guidelines on Sampling.
RangeAQL, Acceptance Number, Consumer Risk (CR), Inspection Level, Lot, Lot Size, Operating Characteristic Curve (OC curve), Probability of Acceptance, Producer’s Risk (PR), Rejectable Quality Level (RQL), Sampling Plan.
Outcome 5
Identify methods used in the New Zealand dairy industry to reduce the cost of true random sampling.
Evidence requirements
5.1Methods used to reduce the cost of true random sampling are explained in accordance with Codex General Guidelines on Sampling and legislative and organisational requirements.
Rangequasi-random sampling, composite sampling, continuous sampling.
5.2An example of where each method is used to reduce the cost of true individual random sampling in the dairy industry is given along with a possible disadvantage of each.
Rangequasi-random sampling, composite sampling, continuous sampling.
Outcome 6
Plot data on Control and CUSUM charts.
Evidence requirements
6.1Additional data given are plotted on given Control and CUSUM charts of the same data.
Rangedata provided are generally within upper and lower limits of control chart, data provided contains a single change of mean.
6.2The point is identified at which a change in mean occurs.
Outcome 7
Estimate the chance of rejection of a lot using an OC curve.
Evidence requirements
7.1The chance of rejection of a lot with x% defective is estimated from a given OC curve.
7.2The proportion of defectives corresponding to a y% probability of rejection is estimated from a given OC curve.
Outcome 8
Determine the number of samples needed for problem solving investigations where a single defect in the sample denotes a problem.
Evidence requirements
8.1From a given formula, the number of samples is determined that must be taken to give at least a x% chance of finding at least one defective if there are y% defectives in the population.
Rangegiven formula is N ≥ [log(1-c)/log(1-d)] (where N is the number of samples required, c is the confidence required, d is the proportion of defects in the population which it is necessary to pick up).
This unit standard is expiring. Assessment against the standard must take place by the last date for assessment set out below.
Status information and last date for assessment for superseded versions
Process / Version / Date / Last Date for AssessmentRegistration / 1 / 28 April 1997 / 31 December 2017
Revision / 2 / 2 July 1999 / 31 December 2017
Revision / 3 / 13 June 2003 / 31 December 2017
Rollover and Revision / 4 / 25 September 2006 / 31 December 2017
Rollover and Revision / 5 / 17 July 2009 / 31 December 2017
Review / 6 / 15 October 2015 / 31 December 2017
Rollover / 7 / 19 January 2017 / 31 December 2018
Consent and Moderation Requirements (CMR) reference / 0022
This CMR can be accessed at
Please note
Providers must be granted consent to assess against standards (accredited) by NZQA, before they can report credits from assessment against unit standards or deliver courses of study leading to that assessment.
Industry Training Organisations must be granted consent to assess against standards by NZQA before they can register credits from assessment against unit standards.
Providers and Industry Training Organisations, which have been granted consent and which are assessing against unit standards must engage with the moderation system that applies to those standards.
Requirements for consent to assess and an outline of the moderation system that applies to this standard are outlined in the Consent and Moderation Requirements (CMR). The CMR also includes useful information about special requirements for organisations wishing to develop education and training programmes, such as minimum qualifications for tutors and assessors, and special resource requirements.
Primary Industry Training OrganisationSSB Code 101558 / New Zealand Qualifications Authority 2018 / / New Zealand Qualifications Aut