FINAL PREP Flashcards
Statistics
Science of making decisions with incomplete knowledge
Population
Entire collection of individual units that share a property or sets of properties from which you want to generalize knowledge about unknown quantities (observations) based on a sub-set of individual units (sample)
Observation (or data point)
Set of one or more quantities (measurements) on a single observation unit (e.g. the weight and height of someone living in Canada that drinks coffee and runs in the morning)
Sample
Subset of observation units
Biological population
All the organisms of the same group or species, which live in a particular geographical area (don’t mix with Statistical population)
Parameter
Quantity describing a statistical population
Estimate (or statistic)
Related quantity calculated from a sample.
Arithmetic mean
Average - it’s a statistical algorithm
Algorithm
Process or set of rules to be followed when calculating a quantity
Important goal in stats?
Infer an unknown quantity!
Variable
Any characteristic, number, or quantity that can be measured or counted (e.g. height, weight, age, gender, eye colour, etc.)
Observation
Contains all the values for the variables of interest
Categorical variables
Describe membership in a category or group; characteristics of observations that do not have magnitude on a numerical scale
Nominal variable
Name - examples:
- Survival (alive or dead)
- Method of disease transmission (e.g. water, air, etc.)
- Eye color (blue, green, etc.)
- Breed of a dog
Ordinal variable
Ordered - examples:
- Life stage (egg, larva, juvenile, adult)
- Snake bite severity score (minimal, moderate, severe)
- Size class (small, medium, large)
Numerical variables
Characteristics of observation have magnitude on a numerical scale
Continuous variables
Can take any real-number values:
- Core body temperature (degrees Celcius)
- Territory size of a bird (hectares)
- Size of fish (cm)
Discrete variables
Only take indivisible units:
- Age at death (years)
- Number of amino acids in a protein
- Number of eggs in a bird nest
Statistical variables
Variables are not based on their measuring units but rather their types (arm length and leg length can be both measured in centimetres but they are TWO different variables).
Random sample - two criteria
1) Every observational unit in the population (e.g. individual fish) have an equal chance of being included in the sample
2) The selection of observational units in the population (e.g. individual fish) must be independent, i.e, the selection of any unit (e.g., individual fish) of the population must not influence the selection of any other unit.
Random sampling advantage
Random sampling minimizes bias of estimates (sample-based value) in relation to a parameter (population value) for a given statistics (e.g., mean fish size)
Experimental study
Researcher randomly assign observational units (fish individuals) to different groups (often called treatments; e.g., high/low protein diet)
Observational study
Researcher has no control over which observational units fall into which groups (e.g. studies on health consequences of cigarette smoking in humans [unethical to assign smoking and no-smoking treatments to observational units])
