Sampling and Probability Flashcards
what is probability?
chance/likelihood of an event occurring
what is the range of values in a probability statement?
between 0 and 1
what is gambler’s fallacy?
belief that if you keep playing, you’ll win
why is gambler’s fallacy false?
chances of winning are the same every time you play
what is the law of large numbers?
if enough people play for a long amount of time, the house (casino) will always win
in calculating birthdays and probability, why does the pairs concept apply?
there are more pairs of people than individuals
what is a population?
entire set of units of analysis
what is a sample?
a subset of the population
what is a statistic?
characteristic of a sample
what is a parameter?
characteristic of a population that always stays the same(realistically unknown)
what should the statistic always mirror as close as possible?
the parameter
what does difference between a statistic and the parameter mean?
error
what are the 3 main challenges in sampling?
- defining the population
- selecting the sample design
- deciding upon sample size
what are the categories of sample design?
probability vs. non-probability
what is probability theory?
everyone has an equal chance of selection for the sample
what is poisson clumping?
certain events clutter together; randomness leads to clumping
what is random selection?
each element has an equal chance of selection independent of any other events in the selection process
what is representativeness?
having the same distribution of characteristics as the population
what is bias?
systematic preference/predisposition to reach a particular conclusion
what is non-probability sampling?
a sample selected in some fashion other than any suggested by probability theory
what are the types of non-random sampling?
- convenience - using only available subjects
- purposive/judgemental - choosing ones you know you need
- snowball - one person leads to another
- quota - predetermined group selection
- selecting informants - choosing person to inform you
when can probability of selection not be determined?
when there’s no mention of sampling error in a study and/or if it can’t be generalized
what is the relationship between sample size and sampling error?
the larger the sample size, the smaller the sampling error
what is an inverse relationship?
a negative relationship, one decreases when one increases
what are the 3 fallacies of sample size?
- needs to be certain proportion of population
- adequate sample size is about 2000
- any increase in sample size increases precision of results
what is sampling error?
difference between a population value and an estimate of that value derived from a sample
what is a probability experiment?
a situation involving chance that leads to a measurable result
what are the requirements of a probability experiment?
- must have more than one possible outcome
- each possible outcome can be specified in advance
- outcome must be due to chance
what is sampling distribution?
distribution of all possible outcomes for a statistic
what is the central limit theorem?
the distribution of a sample’s mean will approach a normal curve as “n” and number of samples increase
