# Shared Flashcard Set

## Details

POLI 181 Statistics Exam 1
for the 1st UNC POLI 181 exam: descriptive statistics, bivariate hypothesis tests, theory and causality, experiments
71
Political Studies
10/15/2011

Term
 What are the two big categories of metrics of data?
Definition
 Discrete and continuous
Term
 What are the sub-categories of discrete?
Definition
 Categorical and Ordinal
Term
 Categorical variables
Definition
 cannot be ranked. e.g., religion, political party affiliation, etc.
Term
 Ordinal variables
Definition
 relates information about which cases havesimilar traits, but allows ranked judgments
Term
 Continuous variables
Definition
 can be ranked and have equal unit distance across their entire range(e.g. income in dollars- each increase by one dollar means the same thing at every point along the range)
Term
 What are two common graphs for categorical variables?
Definition
 Pie chart, bar chart
Term
 What is the only measure of central tendency for categorical variables?
Definition
 The mode- the most frequently occurring category
Term
 What are the two major descriptive goals with continuous variables?
Definition
Term
 What are the two broad classes of descriptive statistics?
Definition
 rank statistics, moment-based statistics
Term
 What is the measure of central tendency for rank-based statistics?
Definition
 The median
Term
 What is the measure of dispersion for rank-based statistics?
Definition
 The IQR: interquartile range
Term
 What is the measure of central tendency for moment-based statistics?
Definition
 The mean
Term
 Which type of data, rank or moment-based, is more sensitive to outliers?
Definition
 Moment-based, because the mean only needs a little bit of an outlier to be thrown off, while the median doesn't break down with outliers
Term
 What are the measures of spread for moment-based statistics?
Definition
 The variance and the standard deviation
Term
 What would happen to the variance if we had no variation in y at all?
Definition
 Variance would equal zero- no spread around the mean.
Term
 What happens to the variance as data are spread further from the mean?
Definition
 The variance increases
Term
 What is the standard deviation?
Definition
 the averagedi erence between values of y and the mean of y
Term
 What are the two key dimensions of dependent variables?
Definition
 Spatial and temporal
Term
 What are two types of research designs (hint: think spatial and temporal)
Definition
 Cross-sectional, time series
Term
 What is cross-sectional data design?
Definition
 Looks at multiple units at one time
Term
 What is temporal data design?
Definition
 Looks at one unit over time
Term
 Why might causality be clearer in a time series?
Definition
 we can examine a phenomenon before and after some independent variable changes
Term
 What kind of causal theories are common with the physical sciences?
Definition
 Deterministic theories: an increase in X by a certain amount will *always* cause anincrease in Y of a certain amount
Term
 What kind of causal theories are more common with humans?
Definition
 Probabilistic: Increases in X cause increases in Y on average
Term
 What is an ecological fallacy?
Definition
 inferring individual behavior frompopulation averages
Term
 What is the first hurdle?
Definition
 Is there something connecting x and y- does it make sense that they might cause one another in a traceable way?
Term
 What is the second hurdle?
Definition
 Does y cause x?
Term
 What is the third hurdle?
Definition
 Do x and y covary?
Term
 What is the fourth hurdle?
Definition
 Can we eliminate any Z's that mightrelate to X and Y and cause Y ?
Term
 Finish this phrase: "While correlation does not mean causation,"
Definition
 Correlation is necessary for causation to exist.
Term
 What is an experiment?
Definition
 a research design in which theresearcher both controls and randomly assigns values of thetreatment (key independent variable) to participants
Term
 What are the two key components of experiments?
Definition
 control, random assignment
Term
 What is a control?
Definition
 The value(s) of the treatment (key independent variable) X are determined by the researcher and not by the participants or nature.
Term
 What two groups comprise the experimental group?
Definition
 Treatment group, control group
Term
 What does randomization control for?
Definition
 for every possible Z regardless of whether we can even list the possible Zs
Term
 Experiments have good ____________ validity but bad ____________ validity.
Definition
 Internal, external
Term
 What is internal validity?
Definition
 The extent to which we can accurately state that the observed independent variable produced the observed effect
Term
 External validity
Definition
 relates to the generalizability of your findings
Term
 What can help with the idea that experiments are low on external validity?
Definition
 replication
Term
 What is an observational study?
Definition
 one in which the researcher does not have control over the quantities of the independent variable (or any variable)
Term
 What is the population of interest in an experiment?
Definition
 the set of units (people, countries, etc. . . ) that the researcher's theory relates to
Term
 What are the two ways to get observational data?
Definition
 Measure the entire population of interest, measure a sample of the population of interest
Term
 What are the two types of data in an experiment?
Definition
 Population data, sample data
Term
 What is population data in an experiment?
Definition
 data about every possible relevant case
Term
 What is sample data in an experiment?
Definition
 a dataset drawn from a subset of cases of some underlying population
Term
 What is a random sample?
Definition
 De ned by the characteristic that everymember of the population of interest has an equal probability of being selected for participation in the study.
Term
 What is a convenience sample?
Definition
 Use participants that are readily at hand
Term
 What is the difference between random assignment and random sampling?
Definition
 Random assignment refers to the decision about whom to give a potential treatment. We randomly assign people to the treatment group from the larger experimental group.Random sampling refers to drawing at random of a sample to study. Usually done (or attempted) in survey research.
Term
 Without experimental control and random assignment, crossing hurdles ___ and ___ of causal evaluation is difficult.
Definition
 2, 4
Term
 What kind of test do you perform if both variables are categorical?
Definition
 Tabular analysis
Term
 What kind of test do you perform if both variables are continuous?
Definition
 Correlation coefficient (Pearson's r)
Term
 What kind of test do you perform if the dependent variable is continuous and the independent variable is categorical?
Definition
 Difference of means
Term
 What kind of test do you perform if the dependent variable is categorical and the independent variable is continuous?
Definition
 N/A
Term
 What do p values range between?
Definition
 0 and 1
Term
 What does the p value show?
Definition
 the probability of randomly finding arelationship in the sample that does not exist in the population
Term
 As the p value approaches ____ we get more confidence that there is a real relationship between the two variables in the population
Definition
Term
 The more data we have, the _____ our p values will be.
Definition
 Lower
Term
 If a p value is less than ____, the relationship is said to be _______ ________.
Definition
 0.05, statistically significant
Term
 What are the three steps to trying to interpret cross tabs?
Definition
 1. Figure out what defines the rows and columns2. Figure out what each cell tells you3. Look for general patterns
Term
 When is Pearson's chi squared (x^2) statistic used? Write it down.
Definition
 Used to find the relationship between two categorical variables.
Term
 How do you calculate the degrees of freedom for the chi-squared statistic?
Definition
 df = (r - 1)(c - 1) where r is the number of rows in your table and c is the number of columns
Term
 When do you use a t-test? Write down the formula.
Definition
 When the dependent variable is continuous and the independent variable is discrete.
Term
 What does the numerator of the t-test formula tell you?
Definition
 the greater the di erence between the means, the higher the value of t will be
Term
 The denominator of the t test requires the _____ ______ of the difference of the two means. Write down how this is calculated
Definition
 Standard error
Term
 How do you calculate degrees of freedom for the t-test?
Definition
 Subtract one from the smaller of the two n's
Term
 When do you use Pearson's r (correlation coefficient?)
Definition
 When both the independent and dependent variables are continuous
Term
 What does covariance mean?
Definition
 That the variables change together
Term
 How do you calculate the covariance between two variables? Write it down.
Definition
 N/A
Term
 If ___ is systematically higher than its mean for the same observations in which ___ is higher than its mean, we'll get a ________ contribution to the covariance.
Definition
 x, y, positive
Term
 How is Pearson's r calculated? Write it down.
Definition
 N/A
Term
 What t-statistic is used to determine whether two continuous variables have a higher correlation than we would expect at random? Write it down. How are degrees of freedom calculated?
Definition
 df = n-1
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