Bell Ringer 1-10-19 Using all available resources, determine the differences and similarities of the following: 1) Population vs. Sample 2) Parameter vs. Statistic 3) Surveys, Experiments, and Observational Studies

Basic Statistics and Sampling Methods Thursday, January 10, 2019

Population vs. sample http://stattrek.com/sampling/populations-and-samples.aspx http://www.dissertation-statistics.com/population-sample.html So… population is the whole group and a sample is a portion of that group.

Parameter vs. statistic http://www.stats.gla.ac.uk/steps/glossary/basic_definitions.html So, a parameter describes the population and a statistic describes a sample.

Surveys, Experiments, and Observational Studies http://pages.csam.montclair.edu/~mcdougal/SCP/Studies_and_Experiments.htm So… survey – collect hopefully random data experiment – do “something” to a sample observational study – just watch, don’t interfere

More vocabulary Inferential & Descriptive https://statistics.laerd.com/statistical-guides/descriptive-inferential-statistics.php Inferential statistics enables you to make an educated guess about a population parameter based on a statistic computed from a sample randomly drawn from that population.

Sampling When conducting a survey, experiment, or observational study, it is almost impossible to survey everyone in a population so people use various sampling methods to gather information. One major concern about sampling methods is whether it is a biased or unbiased method to gather information.

Convenience sampling: Sampling Methods Convenience sampling: when those chosen as a sample of the population are chosen due to ease of collecting data. SIMPLE EASY (first 5 people) NOT a “good” method…

Sampling Methods Random sampling: when everyone in a population has an equal chance of being chosen in the experiment.

Sampling Methods Stratified sampling: when the population is first divided into similar categories and the number of members in each category is determined.

Sampling Methods Systematic sampling: when you determine a method for which to choose members of the population (assign numbers to the population and then choose every 5th person to participate)

Sampling Methods Cluster sampling: when you randomly put the population Into clusters and then choose a Cluster randomly and then randomly choose people in that cluster to participate.

Randomly selecting 10 from all 50 animals Example if selecting 10 animals from 25 dogs, 15 cats, and 10 rabbits Random sampling: when everyone in a population has an equal chance of being chosen in the experiment. Randomly selecting 10 from all 50 animals Stratified sampling: when the population is first divided into similar categories and the number of members in each category is determined. Select 5 from 25 dogs, 3 from 15 cats and 2 from the rabbits Systematic sampling: when you determine a method for which to choose members of the population (assign numbers to the population and then choose every 5th person to participate) Give every animal a random number and then choose every 5th number Cluster sampling: when you randomly put the population into clusters and then choose a cluster randomly and then randomly choose people in that cluster to participate. Randomly put the animals into 2 groups of 25, choose a group, and then choose 10 from that selected group.

Which sampling method is used in the scenario below? A Gallop poll surveyed 1,018 adults by telephone in each region of the country, and 22% of them reported that they smoked cigarettes within the past week. Random Stratified Systematic Cluster

Which sampling method is used in the scenario below? A principal goes to one classroom in each department and chooses two students from each classes to participate in a school climate survey. Random Stratified Systematic Cluster

Which sampling method is used in the scenario below? WSFCS sends out a survey to parents by generating a list of student numbers from PowerSchool. Random Stratified Systematic Cluster

Biased Questions Some questions may use language that people can associate with emotions: How much of your time do you waste on Snap Chat? Some questions may refer to a majority or supposed authority: Would you agree with the NCAE that teachers should be paid more for earning their master’s degree? Phrased awkwardly: Do you disagree with people who oppose the ban on smoking in public places?

Sampling Bias Sampling Bias occurs when one or more sub groups of a population are either over represented or under represented when conducting a survey or experiment. Using the appropriate sampling method for the question reduces bias. Discuss with your partner some examples of bias that could occur when choosing a sample from a population. Be prepared to share your examples.

Margin of Error How good is your data? The margin of error is an interval which tells how many percentage points your data “should” vary from the real population value. The more data you have, the smaller the margin of error. To calculate the margin of error: 𝐸= 1 𝑛 The margin of error (E) = 1 divided by the square root of the sample size.

Examples 1. What is the m.o.e. for a sample size of 30? A “good” result has a m.o.e of ± 3%, so most national opinion polls survey 1,000 people.

Assignment (due tomorrow) Statistics & Sampling Method

Exit Ticket What are the differences between surveys, experiments, and observational studies? What sampling method should you use to do a “good” survey?