Statistics and Sampling Methods: Key Concepts and Study Designs

Statistics

study of procedures for collecting, describing, and drawing conclusion from information

Population

entire collection of indivudal about which information is sought

Sample

subset of population, containing the indidvuals that are observed

Parameter

numerical summary of a population

What is a statistic?

numerical summary based on sample

simple random sample

A sample of size n selected from the population in such a way that each possible sample of size n has an equal chance of being selected.

sample of convienice

sample not drawn by well defined random method

stratified sampling

A type of probability sampling in which the population is divided into groups with a common attribute and a random sample is chosen within each group

cluster sample

obtained by selecting all individuals within a randomly selected collection or group of individuals

systematic sampling

Every nth item in the target population is selected

Voluntary response

sampling design where individuals can choose on their own whether to participate in the sample

ordinal

natural ordering

nominal

no natural ordering

discrete

possible values can be listed, whole #

continous

can take on any value in some interval, unrestricted

randomized experiments

in research, experiments in which subjects are randomly assigned to the conditions that are being studied and compared.

observational study

observes individuals and measures variables of interest but does not attempt to influence the responses

Double-blind experiments

Experiments in which neither the participants nor the people analyzing the results know who is in the control group

randomized block experiment

individuals are first sorted into blocks, and then a random process is used to assign each individual in the block to one of the treatments

cofounder

a variable that is related to both the treatment and the outcome

cohort study

a group is studied to determine whether various facts of interest are associated with outcome

prospective cohort study

subjects are followed over time

cross-sectional cohort study

measurements are taken at one point in time

restrospective c

subject sampled after outcome

skewed to the left

mean < median

skewed to the right

mean > median

matched pairs

A matched pairs design is a type of randomized block experiment in which each block consists of two subjects. There are two treatments, and (one of which may be a placebo). One subject in the block, chosen at random, receives treatment A, and the other receives treatment B.