specific characteristics of the population that a statistical study is designed to estimate.
is a sample in which the relevant characteristics of the sample members match those of the population.
simple random sampling
we choose a sample of items in such a way that every sample of a given size has an equal chance of being selected
we use a simple system to choose the sample, such as selecting every 10th or every 50th member of the population.
we use a sample that is convenient to select, such as people who happen to be in the same classroom
we use this method when we ar concerned about differences among subgroups, or strata, within a population. we first identify the subgroups and then draw a simple random sample with in each subgroup. the total sample consists of all the samples from the individual subgroups.
researchers observe or measure characteristics of the sample members but do not attempt to influence or modify these characteristics
researchers apply a treatment to some or all of the sample members and then look to see whether the treatment has any effects.
in an experiment is the group of sample members who receive the treatment being tested.
lacks the active ingredient of a treatment being tested in a study, but is identical in appearance to the treatment.
refers to the sistuation in which patients imporve simply b/c they believe they are receiving a useful treatment.
if the participants do not know whether thay are members of the treatment group or members of the control group , but the experiments do know.
participants and experimenters do not know who belongs to the treatment group or control group.
margin of error
is used to describe a confidence interval that is likely to contain the tru population paramenter. We find this interval by subtracting and adding the margin of error from the sampl statistic obtained in the study. ie.from = sample stat - margin of error or to = sample stat + margin of error
occurs whenever researchers select their sample in a way that tends to make it unrepresentative of the population.
any item or quantity that can vary or take on different values. In statistics it is the items you seek to measure.
is a bar graph for quantitative data catefories. the bars have natural order and the bar widths have specific meaning.
exists between two variables when higher values of one variable consistently go with higher values of another or when higher values of one variable consistently go wieht lower values of another.