Exam 1 Flashcards
(24 cards)
What is a population?
All possible units we would like to observe but cannot due to constraints such as time, money, and resources.
What is a sample?
A well-chosen subset of the population that we will study. Results obtained from a sample are only interesting because they can be used to understand the population.
What is an estimation?
The process of inferring an unknown quantity of a population using sample data.
A numerical summary calculated for the sample; always known.
What is a parameter?
Quantity describing a population, whereas an estimate is a related quantity calculated from a sample.
A numerical summary calculated for the population; always unkown
What makes a good sample?
Low sampling error (or variation)
-Sampling error is what causes this difference between the estimate and the parameter.
High precision
-Low sampling variation will translate to high precision
Low/No Bias
-Bias is how much the estimate varies from the parameter
Reduce Bias in sampling
What is random sampling?
When every unit in the population has an equal and independent chance of being in the sample. i.e. when every possible subset (sample) from the population is equally likely
What is a categorical variable?
A variable that takes values that fall into pre-specified categories or groups. Don’t have units. and no magnitude on numerical scale.
Ex. Sex chromosome genotype (XX, XY)
Name the two types of categorical variables and describe them.
Nominal: When the categories have no natural ordering.
Ex. Gender, eye color
Ordinal: When the categories have natural ordering.
Ex. Grade (A, B, C) or Size (S, M, L)
What is a numerical variable?
A variable that can be measured/counted. Always has units.
Ex. Core body temp.
What are the two types of numerical variables?
Continuous: Numerical data that take real number values
Ex. Height, Weight
Discrete: Numerical data that take integer values; that can be counted
Ex. Number of people in a household. number of chairs in a room.
What is a population?
Entire collection of individuals or units that a researcher is interested in.
Ex. all the genes in the human genome
What is a sample?
A much smaller set of individuals selected from the population.
Ex. a selection of 20 human genes.
What is sampling error?
The chance difference between an estimate and the population parameter being estimated
What is bias?
A systematic discrepancy between estimates and the true population characteristic
Volunteer Bias
bias resulting from a systematic difference between the pool of volunteers and the population to which they belong. Problem arises when the behavior of the subjects affects whether they are sampled.
Explanatory variable
independent variable
Ex. Examine possibility that high BP leads to an increase in hte risk of strokes
Then high BP is EV
response variable
dependent variable
Ex. Try to predict the risk of stroke from high BP
Then increased risk of strokes = RV
What is an experimental study?
When the researcher assigns different treatment groups of values of an explanatory variable randomly to the individual units of study.
Can determine cause and effect relationships between variables
Ex. Different treatments are assigned randomly to patients in order to compare responses
What is an observational study?
Nature assigns treatment groups or values of an explanatory variable to individuals. Researcher has no control over which units fall into which groups
What is a contingency table?
A frequency table for two (or more) categorical variables
What is a grouped bar graph show?
uses the height of rectangular bars to display the frequency distributions (or relative frequency distributions) of two or more categorical variables.
What is a mosaic plot?
uses the area of rectangles to display the relative frequency of occurrence of all combinations of two categorical variables.
What does a scatter plot show?
An association between two numerical variables
x-axis = explanatory variable y-axis = response variable
What is a mutually exclusive event?
When two events are not simultaneously possible
Pr[A and B] = 0.
Ex. Cannot roll a 2 and a 6 at same time
