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UC-Davis

STA 13

MIDTERM EXAM

STUDY GUIDE

❖ 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

find more resources at oneclass.com

find more resources at oneclass.com