Term

Definition
is a science that involves the extraction of information from numerical data obtained during an experiment or from a sample. It involves the design of the experiment or sampling procedure adn the collection of the data, the analysis of the data, and making inferences about the population based upon information in a sample 


Term

Definition
The entire group of individuals about which the researcher wants information
Examples:
 All United States Citizens
 All male students at VCU
 All sections of all courses taught this semester at VCU



Term

Definition
Some characteristic of the population that the researcher wants to measure
Examples:
1.) Proportion of US citizens who voted in the 2004 presidential election
2.) Average (mean) height of all male students at VCU
3.) Proportion of all sections of all courses taught by adjunct (parttime) faculty 


Term
Greek Letters u(mu) and pi 

Definition
mean is denoted by mu
proportion of successes in a population is denoted by pi 


Term

Definition
A subset of the population that is contacted and examined to gather information
Example: when the population is all male VCU students, a sample would be all male students in this class 


Term

Definition
A descriptive measure, computed from data in a sample, that can be expressed or evaluated numerically.
Example: For the sample of male students in this class, one can compute the average height is a statistic 


Term

Definition
A statement about a population based on the data collected in a sample
Example: To estimate the average height of all male VCU students we can compute the average height of the male students in this class 


Term

Definition
A listing of all the possible values that a characteristic can take and the number (or percentage) of times that each value occurs
Examples:
1.) Gender of student:
Male____
Female____
2.) Color of car:
Blue____
Red____
White____
Other____



Term

Definition
Branch of statistics concerned with numerical and graphical techniques for describing one or more characteristics of a population and for comparing characteristics among populations 


Term

Definition
Branch of statistics in which we use data and statistics computed from a sample to make inferences (statements) about a population
The information used to make these inferences is often some type of descriptive statistic 


Term

Definition
Statistics involve experiments or samples in which either repeated measurements are made on a single subject or measurements are made on many different subjects. This is referred to as replication (or replication). 


Term

Definition
A characteristic whose measurements do not change in repeated trials over time
Example:
1.) Number of days in january each year (always 31)
2.) Number of minutes in an hour (always 60) 


Term

Definition
A characteristic whose measurements vary(or change) from trial to trial or individual to individual
Examples:
1.) Heights of students
2.) Grades on a test 


Term
Qualitative or Categorical Variable 

Definition
A variable whose measurements vary in kind or name, but not in degree. This implies that one level of a categorical variable cannot be considered to be greater than or better than another level
Example: 1.) Gender: male or female
2.) Eye color
3.) Social security number 


Term

Definition
A variable whose measurements vary in magnitude from trial to trial, meaning some order or ranking can be applied to the levels
Examples:
1.) Number of students in a particular class
2.) Weight of a typical student
3.) Grades on a test 


Term
Discrete Quantitative Variable 

Definition
A quantitative varible whose measurements can assumer only a countable number of possible values
Example:
1.) Number of students in a particular class
2.) Number of cars in a parking deck
3.) Grades on a test 


Term
Continuous Quantitative Variable 

Definition
A quantitative variable whose measurements can assume any one of a countless number of values in a line interval. It is usually a measurable quantity or something that is calculated, such as rates, averages, proportions, and percentages
Examples:
1.) Weight of a typical student
2.) Percentage of students who pass a course 


Term

Definition
we select a sample of a population and only measure(or contact) the subjects in the sample 


Term

Definition
The sample should be as representative of the population as possible, meaning that the characteristics of the sample should mimic the characteristics of the population. 


Term

Definition
Bias exists when some subjects or individuals are systematically favored over others. A sample which is representative of the population should be free of bias. If the sample is not representative, then the results will be biased in favor of the responses of those which are overrepresented 


Term

Definition
Selection bias occurs when one or more types of subjects are systematically excluded from the sample.
When selection bias exists, the results from the sample can only be inferred to part of the population. the inference cannot be made to the entire population, but only a subset of the population. This is referred to as undercoverage 


Term

Definition
When an individual randomly chosen to be a part of a sample cannot be contacted or fails (or refuses) to respond, then we have a nonresponse bias. This is often a big problem in surveys or polls, in which the person either throws the survey away or refuses to answer the questions of those conducting the poll. 


Term

Definition
when respondents give inaccurate information or if the interviewer influences the subject to respond in a certain way due to the way the questions are phrased, this is response bias. This is especially a concern with legal or social behavior issues. 


Term
Haphazard or volunteer response sample 

Definition
A haphazard sample involves selecting a sample by some convient mechanism that does not involve randomization.
A mall survey in which questionnaires are distributed to people as they walk through the mall, or a campus survey in which students are questioned as they walk across campus are two examples of haphazard samples. 


Term
A volunteer response sample 

Definition
A volunteer response sample exists when subjects volunteer to be part of the study. Examples include telephone callin polls, internet surveys, newspaper survey, call in talk show surveys, etc.
The problem with volunteer response samples is that often those who choose to respond often have strong opinions, most often negative opinions, and hence volunteer response samples overrepresent those with strong opinions. 


Term

Definition
haphazard and volunteer response samples are particularly prone to bias, particularly nonresponse bias 


Term

Definition
samples in which the subjects are chosen randomly to be in the sample are often representative of the population and are, for the most part, free of bias
When each subject of the population has a positive and equal probability of being selected for the sample, then we are using a probability sampling design to select our sample. this will reduce(or eliminate) bias. 


Term

Definition
with simple random sampling we make a list of all possible individuals in the population and randomly choose n of the subjects in such a way that every set of n subjects has an equal chance of being selected for the sample. This procedure is impartial, meaning the interviewer has no discretion as to whom is to be included in the sample 


Term

Definition
1. Label the individuals in the population from 1 to N.
2. Use a table of random digits, like on page 315, to randomly select a sample of n numbers between 1 and N. These numbers correspond to the individuals who are selected to be in the sample. 


Term
Stratified Random Sampling 

Definition
The population is naturally divided into two or more groups of similar subjects, called strate
Example: Strata 1= males
Strata 2 = females
Simple random samples are then selected from each stratum, and combined to give the complete stratified random sample 


Term
Stratified Random Sampling 

Definition
The number chosen from each stratum should correspond to the percentage of the total population in each stratum, with at least one individual chosen from each stratum 

