population
the entire collection of individual units a researcher is interested in
parameter
a characteristic of a population
sample of convenience
a collection of individuals that happen to be available at the time
variable
characteristic measured on individuals
data
measurements of one or more variables made on a collection of individuals
accurate (unbiased)
on average, gets the correct answer
precise
gives a similar answer repeatedly
sample
subset of individuals/units from a population
estimate/statistic
quantity describing a variable of a sample (e.g. sample mean)
sampling error
chance difference between an estimate and population parameter being estimated
error
random difference between estimate and true population characteristics
bias
discrepancies tending in a certain direction between an estimate and the true population characteristic
properties of a good sample
- sufficiently large
- random
random sample
- each individual has equal probability of being included
- independent selection of individuals
independent sampling
- the chance of an individual being included in the sample is not dependent on others
- the measurement of a sample does not influence the measurement of other samples
examples of non-independence
- catching fish
- repeated measures
measurement bias
systematically over or underestimating a measurement
sampling bias
over-representing portions(s) of a population in a way that biases measurement
measurement error
measurement inaccuracy, generally random difference
sampling error
difference from truth because random sample is not identical to the population
