Basic Statistics Used in Epidemiology

what is a population?

A collection of individuals who share at least one common or organizing characteristic

what is a sample?

subset of the population of interest

what are subjects?

units or individuals of which characteristics are measured

what is a population parameter?

measure computed for the entire population

what is a sample statistic?

measure taken from the representative sample of the population

what are the different types of sampling?

• simple random sampling

• stratified sampling

• systematic sampling

• cluster sampling

• connivence sampling

• snowball sampling

• purposive sampling

• quota sampling

what is stratified sampling?

probability sampling method that divides a population into distinct subgroups, or "strata," based on shared characteristics (e.g., age, income, gender) before randomly sampling from each group

what is systematic sampling?

a probability sampling method where researchers select members of a population at a regular, predetermined interval (n-th element), typically after a random starting point

what is cluster sampling?

a probability sampling method where researchers divide a large population into smaller, heterogeneous groups known as "clusters"—typically based on geography or organization—and then randomly select entire clusters to sample

what is convenience sampling?

a non-probability technique where researchers select participants who are most easily accessible and readily available

what is snowball sampling?

a non-probability, chain-referral technique where existing research participants recruit future subjects from their own network, creating a "snowball effect" that grows the sample size

what is purposive sampling?

a non-probability sampling technique where researchers intentionally select participants or cases based on specific characteristics, knowledge, or experience relevant to the research question

what is quota sampling?

a non-probability sampling technique where researchers create a sample that represents certain population characteristics (like age, gender, or income) by setting specific, predetermined quotas for each subgroup

what are the two types of variables?

qualitative and quantitative data

what is qualitative data?

• categorical: values fall into groups

  • nominal: groups have names (and no order)

  • ordinal: there is an order to the groups

what is quantitative data?

• continuous: has a numeric value

  • Interval (no true zero)

  • ratio (true zero point)

what is range?

difference between highest and lowest number

what is deviation?

difference between each value from the mean

what is variance?

degree of spread within the distribution

what is standard deviation?

square root of the variance

what is a bar chart?

a figure that shows the frequency of cases on the y-axis for categories of a categorical variable on the x-axis

what is a histogram?

a figure with frequency of cases on the y-axis for ordinal (or continuous) variables on the x-axis

• no spaces between values

what are pie charts?

• show proportion of cases according to their category

• used only for categorical variables when you want to show how each variable contributes to the whole

what do contingency tables use?

both categorical variables

what do scatter plots use?

both continuous variables

what is the pearson correlation coefficient (R) ?

statistical measure of association that indicates the strength and direction of a linear relationship between two continuous variables

• used for analysis of scatterplot data

what does an r value of 0 mean?

no association

what does it mean when r approaches either -1 or +1?

the association between the two variables becomes stronger (when r is negative the relationship is inverse)