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Data
collections of observations ( such as measurements, genders, survey responses)

Statiscs
the science of planning studies and experiments, obtaining data, and then organizing, summaraizing presenting, analyzing, interpreting, and drawing conclusions based on the data

population
the complete collection of all individuals (scores, people, measurements, and so on) to be studied; the collection is complete in the sense that it includes all of the individuals to be studied

census
collection of data from every member of a population

Sample
subcollection of members selected from a population

Parameter
a numerical measurement describing some characteristics of a pupulation

statistic
a numerical measurement describing some characteristic of a sample

quantitative data
consists of numbers representing counts or measurements

qualitative data
consists of names or labels; categorical

Quantitative data can either be
discrete or continueous

Discrete data
 result when the number of possible values is either a finite number or a countable number
 (i.e. the number of possible values is 0,1,2,3,...)
Example: The number of eggs that a hen lays

Continuous (numerical) data
result from infinitely many possible values that correspond to some continuous scale that covers a range of values without gaps, interruptions, or jumps

Nominal level
characterized by data that consist of names, labels, or categories only, and the data cannot be arranged in an ordering scheme ( such as low to high)
Example: Survey responses yes, no, undecided

Ordinal level of measurement
involves data that can be arranged in some order, but differences between data values either cannot be determined or are meaningless
Example: Course grades A, B, C, D, or F

Interval level of measurement
like the ordinal level, with the additional property that the difference between any two data values is meaningful, however, there is no natural zero starting point ( where none of the quantity is present)
Example: Years 1000, 200, 1776

Ratio level of measurement
The interval level with the additional property that there is also a natural zero starting point ( where zero indicates that none of the quantity is present); for values at this level, differences and ratios are meaningful
Example: Prices of college textbooks (0$ represents no cost, a $100 book costs twice as much as a $50 book)

Nominal
OrdinalĀ
Interval
Ratio
 Nominal categories only
 Ordinal categories with some order
 Interval differences but no natural starting point
 Ratio differences and a natural starting point

Observational study
observing and measuring specific characteristics without attempting to modify the subjects being studied

Experiment
apply some treatment and then observe its effects on the subjects; (subjects in experiments are called experimental units)

Simple random sample
of n subjects selected in such a way that every possible sample of the same size n has the same chance of being chosen

Systematic sampling
select some starting point and then select every kth element in the population

Convinence sampling
use results that are easy to get

Stratified sampling
subdivide the pupulation in to atleast two different subgroups that share the same characteristics, then draw a sample from each subgroup

Cluster sampling
divide the pupulation area into sections (clusters); randomly select some of those clusters choose all members from selected clusters

Multistage sampling
collect data by using some comination of basic sampling methods
In multistage sample design, pollsters select a sample in different stages, and each stage might use different methods of sampling

Cross sectional study
data are obseved, measured, and collected at one point in time

Retrospective ( or case control) study
data are collected from the past by going back in time ( examine records, interviews,...)

Prospective ( or longitudinal or cohort) study
data are collected in the future from groups of sharing common factors ( called cohorts)

Randomization
is used when subjects are assigned to different gropus through a process of random selection. THe logic is to use chance as a way to create two gropus that are similar

Replication
the repetition of an experiment on more than one subject

Blinding
technique in which the subject doesn't know whether he or she is recieving a treatment or a placebo

Double blind
blinding occurs at two levels:
 1) the subject doesn't know whether he or she is receiving the treatment or a placebo
 2) the experimenter does not know whether he or she is administering the treatment or the placebo

Confouding
occurs in an experiment when the experimienter is not able to distinguish between the effects or different factors

