Statistics Chapter 1 – Flashcards
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Define Statistics [C-O-S-A]
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The science of collecting, organizing, summarizing, and analyzing information to draw conclusions or answer questions while providing confidence in any conclusion
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Define Individual
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A person or object that is a member of the population being studied
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Descriptive Statistics
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Consists of organizing and summarizing information collected
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Inferential Statistics
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Uses methods that generalize results obtained from a sample to the population and measure the reliability of the results
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Define STATISTIC
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A numerical summary of a SAMPLE
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Define Parameter
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A numerical summary of a POPULATION
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Define Variables
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The characteristics of the individuals of the population being studied
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In a national survey of 1300 high school students (grades 9 to 12), 32% of respondents reported that someone had bullied them at school. Is 32% a parameter or a statistic?
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Statistic
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The average score for a class of 28 students taking a calculus exam was 72%. Is 72% a parameter or a statistic?
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Parameter
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Qualitative vs. Quantitative
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Qualitative [Phone Number] Quantitative [Number of Siblings] [Grams of Carbs in Doughnut]
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Continuous vs. Discrete
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Continuous is a decimal [ Length in minutes of a country song] Discrete is a whole number [Points scored by a soccer player in a season]
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Nominal
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If values of variable name, label, or categorize. CAN NOT BE RANKED IN ORDER [Eye Color]
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Ordinal
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Can be ranked in certain order [Movie ratings of one star through five stars]
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Interval
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Addition and subtraction can be performed on the values of the variable [Year of birth of college students] (You wouldn't multiply this-no reason to)
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Ratio
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Multiplication and division can be performed on the values of the variable [Assessed value of a house]
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Observational Study
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Measures the value of the response variable without attempting to influence the value of either the response or explanatory variables. RESEARCHER OBSERVES THE BEHAVIOR OF THE INDIVIDUALS WITHOUT TRYING TO INFLUENCE THE OUTCOME OF THE STUDY
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Designed Experiment
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Researcher assigns the individuals in a study to a certain group, intentionally changes the value of an explanatory variable and then records the value of the response variable for each group [allows researcher to claim causation between an explanatory variable and a response variable]
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What is meant by confounding?
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It exists in a study when the effects of two or more explanatory variables are not separated. So any relation that appears to exist between a certain explanatory variable and the response variable may be due to some other variable not accounted for in the study
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What is a lurking variable?
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Not accounted for in the study but affects the value of the response variable
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What is a cross-sectional study?
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Collect information at a specific point in time
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What is a case control study?
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Retrospective. Individuals that have a certain characteristic in a case control study are matched with those that do not have the characteristics
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What does it mean when an observational study is retrospective?
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Looks at data from the past either through recall or records
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What does it mean when an observational study is prospective?
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Gathers data over time by following the individuals in the study and recording data as they occur
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7th grade students are randomly divided into 2 groups. 1 group is taught math using traditional techniques. The other is taught math using a reform method. After 1 year each group is given an achievement test to compare proficiency. Is this an observational study or an experiment?
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Experiment
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A survey is conducted asking 400 people "Do you prefer coke or pepsi?"
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Observational study
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What is a frame?
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A list of the individuals in the population we are studying
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What does it mean when sampling is done without replacement?
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Once an individual is selected he or she cannot be selected again
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How do you obtain a simple random sample of size 3 from the list of 9?
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You can write each name on paper and choose the names out of hat or number the books 1-9 and randomly select three numbers
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Which sampling method does not require a frame?
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Systematic
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A __ sample is obtained by dividing the population into groups and selecting all individuals from within a random sample of the group
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CLUSTER
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A__sample is obtained by dividing the population into homogeneous groups and randomly selecting individuals from each group
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STRATIFIED
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True or False: When taking a systematic random sample of size n, every group of size n from the population has the same chance of being selected
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FALSE
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True or False: A simple random sample is always preferred because it obtains the same information as other sampling plans but requires a smaller sample size
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FALSE
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True or False: When conducting a cluster sample, it is better to have fewer clusters with more individuals when the clusters are heterogeneous
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TRUE
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True or False: Inferences based on voluntary response samples are generally not reliable
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TRUE
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True or False: When obtaining a stratified sample, the number of individuals included within each stratum must be equal
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FALSE
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Systematic Example
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To estimate the % of defects in a recent manufacturing batch, a quality control manager at Intel selected every 8th chip that comes off the assembly line starting with the 3rd until she obtains a sample of 140 chips
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Cluster Example
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To determine customer opinion of its boarding policy, southwest airlines randomly selects 60 flights during a certain week and surveys all passengers on the flights
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Simple Random Sample Example
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In an effort to identify whether an advertising campaign has been effective, a marketing firm conducts a nationwide poll by randomly selecting individuals from a list of known users of the product
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Convenience Sample Example
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A survey regarding download time on a certain Web site is administered on the Internet by a market research firm to anyone who would like to take it
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Stratified Example
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To determine his DSL Internet connection speed, Shawn divides up the day into four parts: morning midday, evening, and late night. He then measures his Internet connection speed at 5 randomly selected times during each part of the day
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Closed Question?
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Has fixed choices for answers: Easier to analyze limit the response
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Open Question?
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Is a free response question: allow respondents to state exactly how they feel but are harder to analyze due to variety
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What does it mean when a part of the population is under-represented?
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A certain segment of the population is not represented in the sample proportionally to its size in the population
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Distinguish between nonsampling error and sampling error
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Nonsampling is the error that results from UNDERCOVERAGE, NONRESPONSE BIAS, RESPONSE BIAS, DATA ENTRY ERRORS. It is the error that comes from the process of obtaining the data. Sampling is the error that results because a sample is being used to estimate info about a population
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Why is it rare for frames to be completely accurate?
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Frames are obtained periodically whereas populations are constantly changing
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What are some solutions to nonresponse?
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Callbacks, incentives
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Discuss the benefits of having trained interviewers
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Better survey results. Trained interviewers can elicit responses to difficult questions
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What are the advantages of having a presurvery when constructing a questionnaire that has closed questions?
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The researcher can learn common answers
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Experimental Unit
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A person object or some other well defined item upon which a treatment is applied
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Treatment
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Any combo of the values of the factors [explanatory variables]
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Response Variable
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A quantitative or qualitative variable that represents the variable of interest
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Factor
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The variable whose effect on the response variable is to be assessed by the experimenter
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Placebo
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An innocuous medication such as a sugar tablet that looks tastes and smells like the experimental medication
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Confounding
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The effect of two factors on the response variable cannot be distinguished.
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Explain the difference between a single blind and double blind experiment
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Single Blind: the subject doesn't know which treatment is received. Double Blind: neither the subject nor the researcher in contact with the subject knows which treatment is received
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True or False: Generally the goal of an experiment is to determine the effect that treatments will have on the response variable
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True
