Math Notes

survey

researchers ask participants questions about the parameter of interest

observation

researchers observe the behavior of the participants/subjects without trying to influence it in any way

experiment

researchers assign a control and treatment group and manipulate the variables to determine if a relationship between variables exist

law of large numbers

as the sample size gets larger, the average gets closer to the “true/expected” value

correlation

two variables are statistically related, meaning they tend to change together

causation

one variable directly causes a change in another variable

simple random sample

a completely random method, every member of a population has an equal chance of being selected

example of simple random sample

a random number generator is used to select from the entire population

systematic random sample

members of the population are put in order and a starting point is selected at random. after that, every nth member of the population is selected

example of systematic random sample

selecting every 8th customer in a grocery store line. 

stratified random sample

members of the population are grouped and then a certain number of members of each group are random selected

example of stratified random sample

surveying a representative number of students from each year of high school to understand overall opinions. 

cluster random sample

members of the population are grouped and then the groups are randomly selected. each member of the selected group participates

example of cluster random sample

choosing a few random city blocks to survey residents about local services

volunteer sample

anyone in the population can join the sample

example of volunteer sample

asking people to complete a survey on a website about their favorite movies. 

convenience sample

anyone who happens to be available is selected

example of convenience sample

asking colleagues at work about their lunch preferences.