Stats Unit 1 Lesson 3 – Flashcards

The error that occurs when we estimate a population characteristic by looking at only one portion of the population rather than the entire population. (In other words, random sampling error occurs whenever we take a sample to determine characteristics of a population)

The difference between the sample proportion and the 'true' value that would result if a census of the whole population were taken under the same conditions (the population parameter).

- Generally decreases as the sample size increases (but not proportionally) - Depends on the variability of the characteristic of interest in the population - Can be accounted for and reduced by an appropriate sampling plan - Can be measured and controlled in probability sample surveys (surveys of samples of individuals selected by chance).

Can be calculated and is called the margin of error

1/(sq. root(n)) where n = sample size

subtracting the margin of error from and adding the margin of error to the sample proportion eg - 44% +- 6% = 38% to 50%

- Short cut formula only works on random samples (can't use on convenience sample or if have used a voluntary response sample) - Random sample must represent a small portion of the population (sample size must be no more than 1% of the population size)

95% of all samples selected in this way (random samples) would produce an interval estimate that would contain the population parameter. Only about 5% of all samples selected in this way would produce interval estimates that do not contain the population parameter.

Take a probability sample instead of a convenience or voluntary response sample. Probability samples are sample designs that use chance to select the subjects for the sample

Take a larger sample.

Small bias and small variability

Fixed, unknown number that describes the population

Known value calculated from a sample. Can change from sample to sample

In a random sample, each member of the entire population has an equal chance of being selected. In a Simple Random Sample, a group of size n is selected and every possible group has the same chance of being selected.