Sampling (Lecture 3) Flashcards
What are the steps in the scientific method?
Step 1: Identify and define problem Step 2: Define experimental procedure Step 3: Conduct experiment and gather data Step 4: Analyse experimental data Step 5: Propose solution to problem
What is population?
the entire data set that fits your parameters
What is a sample?
a subsection of a population selected using a pre-defined method that can be used for analysis.
What is the definition of a homogeneous material?
same composition everywhere in the material.
What is the definition of a heterogeneous material?
different composition from place to place in a material.
What is the definition of sampling?
the process of collecting a representative sample for analysis
What is the definition of a lot?
the total material from which samples are taken
What is the definition of a bulk sample?
taken from the lot for analysis and must be representative of the lot
What is the definition of a laboratory sample?
a smaller homogenous sample that has the same composition as the bulk sample
What is the definition of an aliquot?
smaller portions of the laboratory sample that are used for individual analyses
What is random sampling?
Totally unbiased sample.
True randomness is hard to achieve.
What is judgemental sampling?
We use prior information about the target population to help guide our selection of samples.
More biased than random sampling, but less samples required.
What is systematic sampling
Sample the target population at regular intervals in space or time.
If a target population’s properties have a periodic trend, a systematic sampling will lead to a significant bias if our sampling frequency is too small.
What is systematic-judgemental sampling?
Prior knowledge about a system is used to guide a systematic sampling plan.
What is judgemental-random (stratified) sampling?
Used for target populations consisting of distinct units, or strata, to minimise sampling bias.
