1.3 Data Collection and Experimental Design

What is replication in an experiment? Why is replication important?

Replication is repetition of an experiment under the same or similar conditions. Replication is important because it enhances the validity of the results

What is the difference between a random sample and a simple random sampling?

With a random sample, each individual has the same chance of being selected. With a simple random sample, all samples of the same size have the same chance of being selected.

What is the difference between a census and a sampling?

A census includes the entire population. A sampling includes only part of the population.

Identify the sampling techniques used and discuss potential sources of bias (if any) explain. After an earthquake, a disaster area is divided into 200 equal grids. Fifty of the girds are selected and every occupied household in the grid is interviewed to help focus relief efforts on what residents require the most. What type of sampling was used? What potential sources of bias were present if any? Select all that apply.

Cluster sampling is used since the disaster area is divided into grids and some of those grids are selected and everyone in those grids is interviewed Bias: - Certain grids may have been much more severely damaged than others. The grids that are selected may not representative in terms of damage - Certain grids may have been much more severely damaged than others. Severely damaged grids may have fewer occupied households.

Assume the population of interest is the student body at a university. Question students as they leave an academic building a researcher ask 383 students about their eating habits What type of sampling was used? What potential sources of bias were present if any? Select all that apply.

Convenience sampling is used because students are chosen due to convenience of location Bias: - The sample only consists of members of the population that are easy to get. These members may not be representative of the population - Because of the nature of the question students may not answer honestly

Determine whether the statement is true or false. If it is false rewrite it as a true statement. The method for selecting a stratified sample is to order a population in some way and then select members of the population at regular intervals

False. The method for selecting a systematic sample is to order a population in some way then select members of the population at regular intervals

Determine whether the statement is true or false. If it is false rewrite it as a true statement. Using a systematic sample guarantees that members of each group within a population will be sampled.

False. Using a stratified sample guarantees that members of each group within a population will be sampled

What is the difference between an observational study and an experiment?

In an experiment, a treatment is applied to part of a population and responses are observed. In an observational study, a researcher measures characteristics of interest of a part of a population but does not change existing conditions.

Observational studies are sometimes referred to as natural experiments. Explain what this means.

In an observational study a researcher measures characteristics of interest of a part of a population but does not change existing conditions

Determine if the survey question is biased. If the question is biased suggest a better wording. How often do you eat vegetables during an average week?

No, because it does not lead the respondent to any particular answer.

Identify the sampling techniques used and discuss potential sources of bias (if any) explain. Chosen at random 620 customers at a restaurant are contacted and asked their opinions for the service they received. What type of sampling was used? What potential sources of bias were present if any? Select all that apply.

Simple random sampling is used since the business is selecting from its customers at a random and all samples of 620 customers have an equal chance of being selected Bias: - The wording of the question asked to the customers may influence them towards a particular response. The results would not be usable in this case

Identify the sampling techniques used and discuss potential sources of bias (if any) explain. In 1965 researchers used random digit dialing to call 1400 people and ask what obstacles kept them from attending town hall meetings. What type of sampling was used? What potential sources of bias were present if any? Select all that apply.

Simple random sampling was used since each number had an equal chance of being dialed so all samples of 1400 phone numbers had an equal chance of being selected. Bias: - Telephone sampling only includes people who had telephones. People who owned telephones may have been older or wealthier on average and may not have been representative of an entire population - Individuals may have not been available when the researchers were calling. Those individuals that were available may have not been representative of the population - Individuals may refuse to participate in the sample. This may have made the sample less representative of the population

Identify the sampling techniques used and discuss potential sources of bias (if any) explain. Tomatoes are planted on a 50-acre field. The field is divided into one-acre subplots. A sample is taken from each subplot to estimate the harvest What type of sampling was used? What potential sources of bias were present if any? Select all that apply.

Stratified sampling is used since the field is divided into subplots and a random sample is taken for each subplot Bias: - Certain subplots may have more or fewer tomato plants than other samples from these subplots may bias the overall sample

Identify the sampling techniques used and discuss potential sources of bias (if any) explain. Every tenth person entering a sporting goods store is asked to choose his or her favorite sport from a list of five different sports that includes a description of each What type of sampling was used? What potential sources of bias were present if any? Select all that apply.

Systematic is used because every tenth person is selected Bias: - The wording of the question may direct respondents towards a particular sport - If there is a regular pattern to the people entering the sporting goods store the sample may not be representative

Determine if the survey question is biased. If the question is biased suggest a better wording. Why is eating eggs good for you?

The question is biased. The wording "How do you think eggs effect your health?" would be better

Determine whether the statement is true or false. If it is false rewrite it as a true statement. A placebo is an actual treatment.

The statement is false. A placebo is a fake treatment

Determine whether the statement is true or false. If it is false rewrite it as a true statement. A double-binding is used to increase placebo effect.

The statement is false. Double-binding is used to decrease the placebo effect.

Determine whether you would take a census or use a sampling to collect data for the study described below. If you would use a sampling determine which sampling technique you would use. Explain. The average height of the 50 residents of a retirement community

The study is a census because the population is small enough for it to be practical to record all of the responses

Determine whether the study is an observational study or an experiment. Explain. To study the effects of social media on teenagers brains researchers showed a few dozen teenagers photographs that had varying numbers of likes while scanning the reactions in their brains

The study is an experiment because it applies a treatment to the teenagers

Determine whether the study is an observational study or an experiment. Explain. In a survey of 1188 adults in a country, 57% said the country's leader should release all medical info that might affect their ability to serve

The study is observational because it does not apply a treatment to the adults

Determine whether you would take a census or use a sampling to collect data for the study described below. If you would use a sampling determine which sampling technique you would use. Explain. The most popular recording artist among 105,000 online movie rental subscribers

The study would use a sampling. The study would use simple random sampling because it would be easy for the company to randomly select a portion of its subscribers