Methods of Data Collection Do an observational study. “What % of RI drivers are talking on their cell phones while driving?”

Methods of Data Collection Perform an experiment. Control Group Placebo Double-blind

Methods of Data Collection Use a simulation – Use of a mathematical or physical model to reproduce the conditions of a situation or process.

Methods of Data Collection Use a survey. Can be conducted by phone, interview or mail. “Do Girls Speed More Than Boys?”  by Joseph B. White and Anjali Athavaley, The Wall Street Journal, May 5, 2010 Allstate Foundation has sponsored a survey that found that young women are not necessarily more responsible than young men – at least in their driving habits. An Allstate spokesman stated, “It would be fair to say the gap is closing,” although “teenage girls continue to be a better risk than boys.”

Survey The data came from online interviews with 1,063 teens across the country in May 2009. About half of the girls felt that they are more likely to drive 10 mph over the speed limit or to phone/text while driving, compared to fewer than 40% of boys for each activity. State Farm, the nation’s largest insurance company, charges 40% more for teenage boys than girls, down from a 1985 gap of 61%. While the company is raising the rates for teenage female drivers, it says that it is raising them based on claims experience and other factors, not these survey results.

Survey wording Be careful about wording: “Do you favor cutting programs such as social security, Medicare, Medicaid and farm subsidies to reduce the budget deficit?”

Which method would you use? A study of the effect on the human digestive system of potato chips made with a fat substitute. A study of the effect of a product’s warning label to determine whether consumers buy the product. A study of how fast a virus would spread in a metropolitan area. A study of the ages of the 535 members of the US Congress.

Census vs Sample A count or measure of an entire population A count or measure of part of a population.

Sampling Error The difference between the results of a sample and those of the population.

Sampling Techniques A random sample is one in which every member of the population has an equal chance of being selected. We will discuss 4 methods of random sampling.

Simple Random Sample Every possible sample of the same size has the same chance of being selected. Example: Select a simple random sample of size 5 from the students in our class.

Stratified Sample Use this method when it is important for samples to have members from each segment of the population. Members of the population are divided into 2 or more strata that share a similar characteristic (ie age, gender, ethnicity, political preference) and we sample randomly from each of the strata.

Cluster Sample Commonly used when the population falls into naturally occurring subgroups, each having similar characteristics. The population is divided into clusters and all of the members of one or more (but not all) of the clusters are selected.

Systematic Sampe Members of the population are assigned a number and then ordered. A starting number is randomly selected, then sample members are selected at regular intervals from the starting number.

A biased sampling method Convenience sample – consists only of available members of the population.

Identify the sampling technique 18. Chosen at random, 500 rural and 500 urban persons age 65 or older were asked about their health and experience with prescription drugs. 20. After a hurricane, a disaster area is divided into 200 equal grids. Thirty of the grids are selected and every occupied household in the grid is interviewed to help focus relief efforts on what residents require most. 22. For quality assurance, every twentieth engine part is selected from an assembly line and tested for durability.

Identify the sampling technique