Part 3 vocab

Question 1

Population

Answer 1

the entire group of individuals or instances about whom we hope to learn

Question 2

Sample

Answer 2

A (representative) subset of a population, examined in hope of learning about the population

Question 3

sample survey

Answer 3

a study that asks questions of a sample drawn from some population in the hope of learning something about the entire population. Polls taken to assess voter preferences are common sample surveys

Question 4

Bias

Answer 4

Any systematic failure of a sampling method to represent its population is bias. Biased sampling method tend to over or underestimate parameters. It is almost impossible to recover from bias, so efforts to avoid it are well spent. Common errors include: Relying on voluntary response, undercoverage of the population, nonresponse bias, and reponse bias.

Question 5

Randomization

Answer 5

The best defense against bias is randomization, in which each individual is given a fair, random chance of selection.

Question 6

Sample size

Answer 6

The number of individuals in a sample. The sample size determines how well the sample represents the population, not the fraction of the population sampled.

Question 7

Census

Answer 7

A sample that consists of the entire population is called a census

Question 8

Population parameter

Answer 8

A numerically valued attribute of a model for a population. We rarely expect to know the true value of a population parameter, but we do hope to estimate it from sampled data. For example, the mean income of all employed people in the country is a population parameter.

Question 9

Statistic, sample statistic

Answer 9

Statistics are values calculated for sampled data. Those that correspond to, and thus estimate, a population parameter, are of particular interest. For example, the mean income of all employed people in a representative sample can provide a good estimate of the corresponding population parameters. The term “sample statistic” is sometimes used, usually to parallel the corresponding term “population parameter”

Question 10

Representative

Answer 10

A sample is said to be representative if the statistics computed from it accurately reflect the corresponding population parameters.

Question 11

SRS (Simple random sample)

Answer 11

A simple random sample of sample size N is a sample in which each set of N elements in the population has an equal chance of selection.

Question 12

Sampling Frame

Answer 12

A list of individuals from whom the sample is drawn is called the sampling frame. Individuals who may be in the population of interest, but who are not in the sampling frame, cannot be included in any sample.

Question 13

Sampling variability

Answer 13

The natural tendency of randomly drawn samples to differ, one from another. Sometimes, unfortunately, called sampling error, sampling variability is no error at all, but just the natural result of random sampling

Question 14

Stratified random sample

Answer 14

A sampling design in which the population is divided into several subpopulations, or “strata”. Random individuals are then drawn from each stratum so that the sample includes individuals from each, often in a representative proportion. If the strata are homogeneous, but are different from each other, stratified sampling can reduce variability in results

Question 15

Cluster Sample

Answer 15

A sampling design in which entire group, or “clusters”, are chosen at random. Cluster sampling is usually selected as a matter of convenience, practicality, or cost. Clusters are heterogeneous, and a random sample of cluster should be representative of the population.

Question 16

Multistage sample

Answer 16

Sampling schemes that combine several sampling methods are called multistage samples. For example, a national polling service may stratify the country by geographical regions, select a random sample of cities from each region, and then interview a cluster of residents in each city.

Question 17

Systematic sample

Answer 17

A sample drawn by selecting individuals systematically from a sampling frame. When there is a no relationship between the order of the sampling frame and the variables of interest, a systematic sample can be representative.

Question 18

Pilot survey

Answer 18

A small trail run of a survey to check weather questions are clear. A pilot survey can reduce errors due to ambiguous quetsions

Question 19

Voluntary response bias

Answer 19

Bias introduced to a sample when individuals can choose on their own whether to participate in the sample. Samples based on voluntary response are always invalid and cannot be recovered, no matter how large the sample size

Question 20

Convenience sample

Answer 20

A convenience sample consists of the individuals who are conveniently available. Convenience samples often fail to be representative because every individual in the population is not equally convenient to sample.

Question 21

under coverage

Answer 21

A sampling scheme that biases the sample in a way that gives a part of the population less representation than it has in the population suffers from undercoverage

Question 22

Nonresponse bias

Answer 22

Bias introduced when a large fraction of those sampled fails to respond. Those who do respond are likely to not represent the entire population. Voluntary response bias is a form of nonresponse bias, but nonresponse may occur for other reasons. For example, those who are at work during the day won’t respond to telephone survey conducted only during working hours.

Question 23

response bias

Answer 23

Anything in a survey design that influences responses falls under the heading of a response bias. One typical response bias arises from the wording of questions, which may suggest a favored response. Voters, for example, are more likely to express support of “the president” than support of the particular person holding that office at the moment.