Lecture 2- Sampling Flashcards
What is sampling?
Predetermined procedure for the selection,withdrawal, preservation transportaion and preparation of the portions to be removed from a lot as samples
Why do we do sampling?
Easier, More cost effective, quicker
Get imformation about LARGE populations
Population
Set of all objects in the system being investigated
Sample
Portion selected froma large quantity of material –> term used for a unit taken from teh total amount of food
Laboratory sample
Sample prepared for testing or analysis
Lot
Quantity of bulk material of SIMILAR composition whose properties are under study
Batch
Quantity of food that is known, or assumed to be produced under UNIFORM conditions
- # should be notes
Unit
Each of the discrete, identifiable portion of food that are suitable for removal from a population as samples that can be individually described, analyzed or combined
Homogenity
The degree to which a property or substance is randomly distrubuted throughout a population
Increment
Individual portion of material collected by a single operation of a sampling device
What are the positive and negative aspects of increasing sample size?
+ Increase accuracy
- Increase time and cost of sampling, handling, analysis and data processing
Why is it important to sample properly?
To avoid:
Consumer risk –> accepting a defective product
Producer risk –> rejecting an acceptable product
What is an example of sampling error?
Sample is not representative of the population
What is an example of a non-sampling error?
Transferring data from the questionnaire
What is variance?
An estimate of the uncertainty
What is total variance?
Sum of variance at each step
What is an example of error at... at the 1. Sample collection 2. Sample preparation 3. Laboratory analysis 4. Data processing 5. Interpretation
- Sampling error
- Erroneoud sample preparation
- Manual or intrument error
- Erroneous data handling
- Erroneous inference
What ar ethe two types of sampling plans?
Probability and non-probability plans