Stats - Collecting Data Flashcards
Convenience Sampling
Sampling in convenient places leaving you with not very accurate results
- ex. sampling about cafeteria food on the cafeteria line - the people on the line would give it a good rating
Bias
Systematically favoring a different outcome
- Sampling not randomly
- Choosing the people you sample which can lead to a different outcome because you can be choosing people that you think will give you a certain answer
Voluntary Response Sampling
Allows people to choose to be in the sample by responding to a general information
- Doesn’t require you to answer and it takes time so most people wont respond
- People who respond either really love it or really hate it - strongly opinionated people (usually negative responses)
- Someone who didn’t get their way
- Response bias
Random Sampling
Involving using a chance process to determine which members of a population are included in the sample
- Chosen with no bias/influence by the holder
Simple Random Sample (SRS)
Size of n is chosen in such a way that every group of n individuals in the population has an equal chance to be selected in the sample
N = population
n = Sample size (>1)
- Multiply to get the amount of combinations
Permutation
Used to see how many ways you are able to arrange something
-ex. 4 books on a shelf (4x3x2x1)
Census
Collects data from every individual in the population
Cluster Sampling
Selects a sample by randomly choosing clusters
Strata
Groups of individuals in a population who share characteristics thought to be associated with the variables being measured in the study
Systematic Sampling
Selects a sample from an ordered arrangement of the population by randomly selecting one of the first k individuals and choosing every kth individual there after
Random
everyone has an equal chance
Under coverage
When some members of the population are less likely to e chosen or cannot be chosen in a sample
- ex. having a survey on a Monday at 12 pm - excludes everyone at school or work
Nonresponse
When an individual chosen for the sample can’t be contacted or refuses to participate
- may not answer - makes it not random anymore
- gives you less accurate results
- leads to response bias
Response Bias
When there is a systematic pattern of inaccurate answers to a survey question
- someone obviously favoring a side
- agreeing just to be left alone
- leads to inaccurate results
- may not be intentional - they may not know the answer at the top of their head
- Someone may be messing around on the survey
Observational Study
Observes individuals and measures variables of interest but does not influence the response
- Data that is already collected to see the results (research)
- Not doing anything to affect the outcome or manipulate
Response Variable
Measures an outcome of a study
- The change
- Similar to an dependent variable
Explanatory Variable
May help or predict changes in a response variable
-What you think will cause the change
- Similar to an Independant variable
Confounding Variable
Occurs when two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other
- Also known as the lurking variable
- A variable that could possibly effect the outcome
Placebo
A treatment that doesn’t have any active ingredient, but is otherwise like other treatments
- A dummy treatment
- Control variable
Treatment
A specific conditions applied to the individuals in an experiment
Experimental Unit
Object to which a treatment is randomly assigned
Subjects
Often a name for experimental units that are human beings
Control Group
Control the confounding variables used to provide a baseline for comparing the effects of other treatments
Double-Blind
Neither the subjects nor those who interact with them and measure the response variable know which treatment a subject is receiving
