Exam (elaborations)
STRAIGHTERLINE INTRODUCTION TO STATISTICS
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STRAIGHTERLINE INTRODUCTION TO STATISTICS
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STRAIGHTERLINE INTRODUCTION TO STATISTICSFour steps in the process of statistics - answer- 1. Producing Data
2. Exploratory Data Analysis
3. Probability
4. Inference
Categorical variable - answer- places individuals into one of several groups
Two types: nominal and ordinal
Quantitative Variable - answer- represents a measurement or a count
Two types: Interval and ratio
Nominal Variable - answer- categorical variables where there is no natural order among the categories
Ordinal variable - answer- categorical variables where there is natural order among the categories
Interval Variable - answer- a measurement or count for which it makes sense to talk about the difference between values, but it does not make sense to talk about the ratio between values; 0 does not represent the absence of quanitity
Interpreting Scatterplots:
Extrapolation - answer- Prediction for ranges of the explanatory variable that are not in the data; is not reliable and should be avoided
Association (does/does not) imply causation. - answer- Does not
Lurking Variable - answer- a variable that is not among the explanatory or response variables in a study, but could substantially affect your interpretation of the relationship among those variables
Simpson's paradox - answer- When a lurking variable causes you to rethink the direction of an association
Probability sampling plan - answer- any sampling plan that relies on random selection (avoids bias).
Simple Random Sampling - answer- Every member of the population has an equal probability of being selected for the sample
Cluster Sampling - answer- Used when the population is naturally divided into groups. Take a random sample of clusters and use all individuals within those clusters as the sample. Stratified sampling - answer- Used when the population is naturally divided into sub-
populations called stratum. Choose a simple random sample from each stratum and use
these together as the sample.
Multistage sampling - answer- a probability sampling technique involving at least two stages: a random sample of clusters followed by a random sample of people within the selected clusters
Observational study - answer- values of the variable or variables of interest are recorded as they naturally occur; no interference
Sample surveys - answer- a particular type of observational study in which individuals report variables' values themselves, frequently by giving their opinions.
Experiment - answer- researchers "take control" of the values of the explanatory variable because they want to see how changes in the value of the explanatory variable affect the response variable
The Complement Rule - answer- P(not A) = 1 - P(A)
useful for finding events of the type "at least one of..."
General Addition Rule - answer- P(A or B) = P(A) + P(B) - P(A and B)
used to find events of the type events of the type "A or B"
General Multiplication Rule - answer- P(A and B) = P(A) * P(B | A)
Used for events of the type "A and B"
or when A and B are independent: P(A and B) = P(A) * P(B)
Conditional probability P(B | A) - answer- the conditional probability of event B occurring given that event A has
occurred
P(B | A) = P(A and B) / P(A).
Methods for checking for independence of two variables - answer- If the two variables are independent:
· P(A|B)= P(A)
· P(B|A)=P(B)
· P(B|A)=P(B| not A)
· P(A and B)= P(A) * P(B)
1. Discrete random variable
2. Continuous random variable - answer- 1. things we count
2. things we measure
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