What is a simulation?

MIMICS REALITY.. In this class, using random numbers to show how random real world events may occur.

You want to simulate the likelihood of more than 4 psychology majors being on a full bus that seats 30. 1 in 9 students are psych majors.

use single digits on a random number table. Each digit represents a student on the bus. Ignore the zeros. Let 1 be a psych major, and 2 through 9 be other students. Trials end when you have reached 30 students. Count the number of psych majors (ones) in the trial. Record this. Do this 20 times. Find the percent of times there were 4 or more psych majors on the “bus.” If this occured in 5 trials.. then the likelihood is 5 in 20, or 25%

What is the response variable in a simulation

If you are wondering “how many batteries do you have to check to to find 3 bad batteries?” the response variable is “average number of batteries you checked” in the trial. If you are wondering “how many failed septic systems can be expected on a street of 10 houses?” the response variable is “the average number of failed systems” in the trial.

What are some sampling methods?

SRS, stratified, clustered, systematic , convenience

What is a quality of SRS that is not a quality of Systematic, Stratified or Clustering?

n an SRS, all groups are possible, and ALL POSSIBLE GROUPS have the same chance of being picked (like all senior male students.).The other methods have lots of “impossible groups” SRS has no impossible groups.-Stratified- an impossible group would be all girls (you’re taking some boys and girls)-Clustered- an impossible group would be all girls (each cluster has boys and girls)-systematic- an impossible group would be 4 people that are right next to each other

what is a simple random sample

ALL THE SUBJECTS IN A HAT!!! (or all names or numbers, if not, you’d need a large hat). A sample where every possible group has the same chance of becoming a part of a sample. You could get “all males”

What is response bias and how do you avoid it?

Response bias is any influence that may sway the respondent to give a more favorable answer e.g wording of the question, interviewer’s behavior/background. Therefore, in a survey, ask questions that allow respondents to answer comfortably and honestly. Keep the wording “indifferent” or neutral in some way in order to unduly favor one response over another.

What is sampling error?

IT IS NOT A MISTAKE!!! Because the data in samples are generally different, the statistics calculated from one sample to another vary and are generally not equal to the parameter. This variablilty of the STATISTICS is called sampling error. (not the variability of the data).

Does a sample of 128 people tell you more about a population of 1000 people or a million people?

It will tell you just as much about both. Same reliability (if sample is representative)

What is statistically significant?

When an observed difference is too odd for us to believe that it is likely to have occurred naturally (or just randomly). Basically it is Statistically Significant when we don’t think it happened randomly. when you think “something’s up” or “something’s fishy”

What is systematic sampling?

EVERY Nth. TOTAL POP/SAMPLE SIZE= your n. Randomly choose first. RANDINT(1, n). And then take every NTH.

What is the difference between non response bias and undercoverage?

You may ask someone to take a survey, they may say no. They may feel differently than the people who decide to take the survey. In this case, that is non-response bias. Undercoverage happens when you didn’t even ask some people to take the survey. The people you didn’t even ask might feel different.

What is the difference between response bias and nonresponse bias?

Response is when the person’s response is influenced by the question or questioning method (like if a parent asks if you use drugs, as opposed to a friend… there is only one answer to this, but one might respond differently to them), non response is is when the people who don’t respond might have different opinions/views than the people who did.

What is the problem with convenience sampling?

The sample may not be representative as it is not randomized to include every type of person. Friends and family are convenient but they likely share similar opinions and thus the sample is not representative of a population.

What is undercoverage?

Undercoverage is when a group of the population is not represented in the sample.

What is the difference between a stratified and a cluster sample?

Stratified- you divide the population up into groups according to traits, called strata (groups with similar traits- homogeneous groups) and randomly choose a few from each strata.

Cluster- grab clusters of the population. each cluster should be like the population. use the whole cluster (usually)

what are two differences between observational studies and experiments?

- Experiments can prove causation (studies can’t) . 2. In experiments, you assign treatments (studies you just watch)

what is a factor?

A variable in an experiment that the experimenter manipulates (like sleep)

What is a level in an experiment?

A level is a specific value(s) that the experimenter chose for a factor that is manipulated.ex. Factor is sleep, level(s) would be how many hours the subjects were aloud to sleep.. 4 hours, 6 hours, 8 hours.. 3 levels