Populations, Samples, Variables Flashcards
population
collection of things having some quantifiable characteristic in common
inclusion criteria
common characteristics of a population (what they HAVE to have)
exclusion criteria
common characteristic members of a population lack (what they CAN’T have)
internal validity
the study was done right
external validity
the study means something
sample
a group of individuals that represents the population
random sampling
every member of the population has an equal chance at being selected
Law of Independence
selection of one member does not influence the chance of choosing any other
parameter
a true numerical value the summarizes the data; stable but not constant
statistic
estimate of a parameter in a sample
confidence interval
statistic +/- margin of error
Relationship between Sample Size and CI?
Larger sample size = narrower CI
3 Descriptions of Variables
- Type
- Scale of Measurement
- Distribution of Values
3 Types of Variables
- Qualitative
- Quantitative
- Categorical
5 Scales of Measurement
- Binary
- Nominal
- Ordinal
- Interval
- Ratio
The Two Main Categories of Distribution Patterns
- Normal/Gaussian (parametric)
- Nonparametric
Quantitative Variable
numbers that reflect a value
can be discrete (1 through 5) or continuous (wide range)
Categorical Variable
no numerical value EVEN IF categories have been assigned a number
3 Scales within Categorical Variables
- Binary/dichotomous (yes/no, present/absent)
- Multinomial/nominal (coat color, eye color)
- Ordinal (small/medium/large)
distribution
pattern seen when you graph the frequency of the variable’s different values
Normal Distribution
pretty lil bell curve, describe with mean and standard deviation (95% of observations fall within 2 standard deviations of the mean)
How to describe nonparametric distributions?
median and percentiles
p-value
used to determine if a change we observed is real or if it just happened by chance
