allow for classification of individuals based on some attribute or characterisitic
discrete variable
a quantitative variable that has either a finite number of possible values or a countable number of possible values. the term countable means that the values result from counting, such as 0,1,2,3,4 and so on.
Continuous data
a quantative variable that has an infinite number of possible values that are not countable. Example 0.023,1.25
Quantative data
are observations corresponding to a quantative variable
sample size
n=size of sample
Observational study
measures the value of the response variable without attempting to influence the value of either the response or explanatory variables. That is, an observational study, the researcher observes the behavior of the individuals in the study without trying to influence the outcome of the study.
rats are exposed to cell phone waves for a period of time to see if the cell phone waves cause brain tumors. after a period of time the rats are examined. this study is called...
Observational study
Census
is a list of all individuals in a population along with certain characteristics of each individual.
Random Sampling
the process of using chance to select individuals from a population to be included in the sample.
the key to obtaining a sample representative of a population to let chance or randomness play a role in dictating which individuals are in the sample. this is called
random sampling
simple random sampling
a sample of size n from a population of size N is obtained through sample random sampling. If every possible sample size of n has an queally likely chance of occuring the sample is then called simple random sampling.
Stratified sample
is obtained by seperating the population in nonoverlapping groups called strata and then obtaining a simple random sample from each stratum. The individuals within each stratum should be homogeneous in some way.
systematic sample
is obtained by selecting every kth individual from the population. the first individual selected corresponds to a random number between 1 and k
cluster sample
is obtained by selecting all individuals within a randomly selected collection or group of individuals.
a teacher wants to learn the characterisitics of students enrolled in online classes. The teacher can treat each class as a cluster and obtain a simple random sample in those classes. This is called...