# [STA 13] - Midterm Exam Guide - Ultimate 26 pages long Study Guide!

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7 Feb 2017
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UC-Davis
STA 13
MIDTERM EXAM
STUDY GUIDE
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Statistics: study of methods used to learn about the world from data
Data: collection of observations
In biological sciences usual focus is on human data
We use statistical methods to
Test theories
Make predictions
Understand relationships between variables
Use stats to make decisions
Medical purposes (which drug to use)
Business ( how much to produce)
Government policy
Data comes from many forms
Surveys
Experiments
Routinely collected
Medical records
Government employment, income)
Cancer registries (track different types of cancer)
Statistics is
Collecting data
How do we chose the people to participate?
Methods include random sampling and non-random sampling
Experiments
How do we choose who gets which treatment?
Randomized clinical trial
A type of experimental study where treatments are randomly
assigned to subjects
Need to now sampling methods and experimental design to
decide which statistical method to use and how to interpret
results
Summarizing and presenting data
graphs(bar charts, histograms, scatter plots)
Descriptive statistics
Numbers used to describe some characteristic of the data
Ex: mean, standard deviation,
Analyzing and interpret data
Drawing conclusions from data
This is called inferential statistics
Use data to “infer” something about how things work
Ex: Identify relationships between variables, estimate
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Parameters determine cause and effect
5 important definitions
Population: a collection of items or individuals we’re interested in
Census: collection of data from every member in population
Sample- a subset of population which is either selected or available
for taking measurements
We rarely have a census, so usually need to learn about the
population from a sample
Parameter - a numeric description of some characteristic of
population
Ex: average (mean), average age, percent males
Statistic - numeric description of some characteristic of the sample
Any function of the sample data is a statistic
Ex: mean, standard deviation, max value
We use the value of a statistic (from the sample) to estimate the value of
the parameter (in the population)
Use the statistic from the sample to estimate the parameter in the
population
Example: want to estimate average age of students in Stat 13C
7 students in first row
Average age 19 yrs old
Population - all 200 students
Sample - 7 students in front row
Parameter - average of all 200 students
Statistic - average age of 7 students = 19
Why might this statistic not be a good estimate of the parameter?
Small sample size
population
Collect data
Sample
calculate
statistic
estimate
parameter
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