data gathering techniques samples and surveys. 2 types of data 1. numerical 2. categorical

Data Gathering Techniques

Samples and Surveys

2 Types of Data

1. Numerical 2. Categorical

Numericalexamples include things likehow many, height, weight,

salary, etc

Categoricalexamples include things likewhat kind,what type,what color,etc

Population

all members of a set

Sample

Part of a Population

If you determine a sample carefully, the statistics for the sample can be used to make general conclusions about the larger population.

Sampling Types

Methods used to select samples • Convenience• Self-selected• Systematic• Random

Convenience Sample

select any members of the population who are conveniently and readily available

Self-selected sample

select only members of the population who volunteer for the sample

Systematic sample

order the population in some way, like alphabetically, and then select from it at regular intervals

Random sample

all members of the population are equally likely to be chosen

BiasA systematic error introduced by the sampling method.A sample has a bias when a part of a population is overrepresented or underrepresented

Identify the sampling method.Determine if there is any bias.

A newspaper wants to find out what percent of the city population favors a property tax to raise money for local parks.

A newspaper article on the tax increase invites readers to express their opinions on the newspaper’s website.

Identify the sampling method.Determine if there is any bias.

A newspaper wants to find out what percent of the city population favors a property tax to raise money for local parks.

A reporter interviews people leaving the city’s largest park.

Identify the sampling method. Determine if there is any bias.

A newspaper wants to find out what percent of the city population favors a property tax to raise money for local parks.

A survey service calls every 50th listing from the local phone book.

Identify the sampling method.Determine if there is any bias.

The students planning the junior class party want to know what kinds of pizza to buy. They ask the pizza restaurant what kinds sell the most.

Study Methods

another way to collect sample information is to perform a study

observationalcontrolledsurvey

Observational study

measure or observe members of a sample in such a way that they are not affected by the study

Controlled experiment

Divide the sample into 2 groups.Impose treatment on one group but not on the other “control” groupThen compare the effect on the treated group to the control group.

Survey

Ask every member of the sample a set of questions

analyzing study methods

Which type of study method is described in each situation?Researchers randomly choose two groups from 10 volunteers. Over a period of 8 weeks, one group eats ice cream before going to sleep, and the other does not. Volunteers wear monitoring devices while sleeping, and researchers record dream activity.Should the sample statistics be used to make a general conclusion about the population?

analyzing study methods

Which type of study method is described in each situation?

Students in a science class record the height of bean plants as they grow.

Should the sample statistics be used to make a general conclusion about the population?

analyzing study methods

Which type of study method is described in each situation?

Student council members ask every 10th student in the lunch line if they like the cafeteria food.

Should the sample statistics be used to make a general conclusion about the population?

analyzing study methods

Which type of study method is described in each situation?

A pharmaceutical company asks for volunteers to test a new drug to treat high blood pressure. Half the volunteers will be given the drug, and half will be given a placebo. The researcher will monitor the blood pressure of each volunteer.Should the sample statistics be used to make a general conclusion about the effectiveness of the drug in the larger population?

Designing a survey

SPORTS During the 2008 Olympic Games, a U.S. swimmer won more medals than any other swimmer in history. What sampling method could you use to find the percent of students in your school who recognize that swimmer from a photograph.

survey question

SPORTS During the 2008 Olympic Games, a U.S. swimmer won more medals than any other swimmer in history. What is an example of a survey question that is likely to yield information that has no bias?

ADDITIONAL PROBLEMS

GIVE TYPE OF SAMPLING METHOD

DOES THE SAMPLE HAVE A BIAS?

Politics

A political candidate wants to know what percent of his constituency favors a Referendum A on an upcoming ballot election. His staff asks each person who comes into the candidate’s office for 3 days whether they support Referendum A.

Management

The manager of a grocery store wants to determine what percent of shoppers use store coupons.He asks every 10th shopper who passes through the store’s door for the next week if he or she intends to use a store coupon on his or her visit.

study method? use stats?

Scientists study the effects of the phases of the moon on the levels of low tide and high tide in 200 coastal cities in the U.S. for a period of 12 months.

study method? use stats?

A pet food company randomly chooses two groups of 20 puppies for a study. One group eats a new brand of dog food and the other group eats an off-brand of dog food for a period of 4 weeks. Researchers record muscular and skeletal growth rates in both groups.

study method? use stats?

For a class project, students in Health class ask every tenth student entering the school if they eat breakfast in the morning.

NCFE type question

To determine the most popular brands of tea consumed by Americans, a survey is conducted in a busy downtown location at lunch time.

Which of the following is NOT a potential bias in the sampling method?

least biased

a. Urban office employees are not representative of the general population.

b. The results could be influenced by national brand teas available in the area.

c. A lunchtime survey does not reflect peoples’ tastes at other times of the day.

d. The survey must include call-in and online responses.

Take note of samples and surveys used in different places.

math is everywhere