Collecting Data

Collecting Data

Steps in a statistical study

• Identify the variable being studied and population

• Choose a sample that represents the population

• Collect data

• Organize and describe data

• Interpret and draw conclusions

Types of Samples

• Self-selected

• Systematic

• Stratified

• Cluster

• Convenience

Self-selected

Volunteers

Example: Put survey on social media and ask people to participate

Systematic

Use a rule to select

Example: Survey every 5th customer

Stratified

Population is divided into smaller groups and people are selected randomly from each group

Example 1: Splitting the United States into regions and selecting people from each region

Example 2: Separating the population by age groups and selecting people from each age group

Cluster

Population divided into different groups and all members of that group are selected

Example: Grouping students by school and then randomly selecting one of the schools to survey

Convenience

Select members that are easy to reach

Example 1: Survey people in your class

Example 2: Survey people who live on your street

Multiple Choice

Determine the sampling method:

A psychologist is studying the sleep patterns of 4000 students at her university. She assigns each student a number and selects the sample by choosing every 50th number

• Stratified

• Cluster

• Convenience

• Systematic

Multiple Choice

An electronics manufacturer wants to know customers opinions about a new media player. Emails with online surveys are sent to customers who purchased one.

• Stratified

• Cluster

• Convenience

• Systematic

Multiple Choice

You want to determine if people in your neighborhood like the new neighborhood website. You randomly select a neighbor from each block.

• Convenience

• Stratified

• Cluster

• Self-selected

Multiple Choice

The principal asks students at one lunch table about the quality of food.

• Stratified

• Cluster

• Convenience

• Systematic

Recognizing Bias

• Unbiased Sample: Represents entire population; Valid

• Biased Sample: Over- or Under-represents part of the population; Invalid

Multiple Choice

A computer science teacher wants to know how often students at a school access the Internet. The teacher uses a sample of students from one of her computer classes.

• Biased

• Unbiased

Multiple Choice

Would you rather watch an award winning movie or just read some book?

• Unbiased

• Biased

Multiple Choice

Your school principal randomly selects 5 students from each grade to complete a survey about school spirit.

• Biased

• Unbiased

Methods of collecting data

• Experiment

• Observational Study

• Survey

• Simulation

Multiple Choice

Identify the data collection method:

A park ranger measures and records the heights of trees in a park as they grow.

• Experiment

• Observational

• Simulation

• Survey

Multiple Choice

A researcher uses a computer program to help determine how fast a virus might spread within a city.

• Survey

• Experiment

• Simulation

• Observational Study

Multiple Choice

A researcher places bacteria samples in two different climates. The research then measures the bacteria growth in each sample after 3 days.

• Simulation

• Experiment

• Observational Study

• Survey