### response variable

values of this variable record the results of each trial with respect to what we were interested in

### nonresponse bias

bias created when people who are randomly selected refuse to particiapte in the sample

### matched design

when our data values are not independent of one another and are related somehow to one subject - it is a form of blocking

### population parameter

mathematical measures taken from the entire population like the population mean and standard deviation

### sample statistics

mathematical measures taken from a sample of the population of interest like the sample mean and sample standard deviation

### simple random sample

abbreviated SRS, this requires that every item in the population has an equal chance to be chosen and that every possible combination of items has an equal chance to exist. No grouping can be involved.

### stratified random sample

population is divided into homogenous groups and then a random sample is drawn from each group

### cluster sample

population is split into parts or clusters usually based on geography and then entire clusters are selected randomly and sampled

### systematic sample

a sample is drawn from the population by following a systematic plan to give every object in the population an equal chance to be chosen but all possible groups can not be formed

### multistage sampling

sampling schemes that combine several different sampling methods at different stages

### observational study

a study based on data where no manipulation of factors has been employed, we simply observe what has or will happen

### factor

a variable whose levels are controlled by the experimenter to discover its effects on the subjects

### control group

a group created the provide a basis for comparison usually either an old or placebo treatment

### single blind

when the subjects in an experiment do not know if they are in the treatment or control group

### double blind

when the subjects as well as those evaluating the result of an experiment do not know which subjects are in the treatment or control groups

### placebo

a fake treatment often given to the control group to help prevent the placebo effect (subjects improving by the power of suggestion)

### blocking

subjects or experimental units are grouped together homogeneously because of some charcteristic they have in common that is believed might effect the experiment

### confounding

when the results of an experiment can be determined because a variable has not be accounted for and has interferred with your results

### convenience sampling

a poor way to collect a sample - do what is convenient for the surveyor, data is usually very biased