# STA 2023 Lecture Notes - Lecture 9: Statistical Inference, Descriptive Statistics, Simple Random Sample

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12 May 2019
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Department
Course
Professor
data
Consist of information coming from observations, counts, measurements, or
responses.
statistics
The science of collecting, organizing, analyzing, and interpreting data in order to
make decisions.
population
The collection of all outcomes, responses, measurements, or counts that are of
interest.
sample
A subset, or part, of the population.
parameter
A numerical description of a population characteristic.
statistic
A numerical description of a sample characteristic.
descriptive statistics
Involves organizing, summarizing, and displaying data.
e.g. tables, charts, averages
inferential statistics
Involves using sample data to draw conclusions about a population.
qualitative data
Consists of attributes, labels, or non numeric entries.
quantitative data
Numerical measurements or counts.
nominal level of measurement
- qualitative data only
- categorized using names, labels, or qualities
- no mathematical computations can be made
ordinal level of measurement
- qualitative or quantitative data
- data can be arranged in order, or ranked
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- differences between data entries is not meaningful
internal level of measurement
- quantitative data
- data can ordered
- differences between data entries is meaningful
- zero represents a position on a scale (not an inherent zero - zero does not imply
"none")
ratio level of measurement
- similar to interval level
- zero entry is an inherent zero (implies "none")
- a ratio of two data values can be formed
- one data value can be expressed as a multiple of another
observational study
A researcher observes and measures characteristics of interest of part of a
population.
experiment
- A treatment is applied to part of a population, called a treatment group, and
responses are observed.
- Another part of the population may be used as a control group, in which no
treatment is applied. (The subjects in both groups are called experimental units.)
- In many cases, subjects in the control group are given a placebo, which is a
harmless, fake treatment that is made to look like the real treatment.
simulation
Uses a mathematical or physical model to reproduce the conditions of a situation
or process.
survey
- An investigation of one or more characteristics of a population.
- Surveys are carried out on people by asking them questions.
- Commonly done by interview, Internet, phone, or mail.
confounding variables
Occurs when an experimenter cannot tell the difference between the effects of
different factors on a variable.
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