Statistics 1.3 Simple Random Sampling/ 1.4 Other Effective Sampling Methods

A internet site asks its members to call in their opinion regarding their reluctance to provide credit information online. What type of sampling is used?

Convenience

When taking a systematic random sample of size n, every group of size n from the population has the same chance of being selected?

False, because certain groups would never be selected

Stratified and cluster samples are different

In stratified sample, we divide the population into two or more homogenous groups. Then we obtain a simple random sample from each group. In a cluster sample, we divide the population into groups, obtain a simple random sample of some of the groups and survey all individuals in the selected group

Toshiba wants to administer a satisfaction survey to its current customers. Using their customer​ database, the company randomly selects 9090 customers and asks them about their level of satisfaction with the company. What type of sampling is used?

Simple random

frame

a list of all the individuals within a population

sample with replacement

a selected individual is placed back into the population and could be chosen a second time

convenience sample

is a sample in which the individuals are easily obtained and not based on randomness Studies that use convenience sampling generally have results that are suspect. The results should be looked on with extreme skepticism yield unreliable results because the individuals in the survey are not chosen using random sampling

to determine her heart rate, Keri divides up her day into three parts: morning, afternoon, and evening. She then measures her heart rate at 4 randomly selected times during each part of the day. What type of sampling is used?

stratified

Homogeneous Cluster (similar individuals)

is clusters have homogeneous individuals it is better to have more clusters with fewer individuals in each cluster. Homogeneous (similar individuals) Heterogeneous clusters (dissimilar individuals)

stratified sample

is obtained by separating the population into non overlapping groups called strata and then obtaining a simple random sample from each stratum. The individuals within each stratum should be homogeneous (or similar) in some way. is obtained by dividing the population into homogenous groups and randomly selecting individuals from each group advantage of stratified sampling over simple random sampling is that it may allow fewer individuals to be surveyed while obtaining the same or more information.

self-selected sample (aka voluntary response samples)

members of the population select themselves by volunteering to participate in the survey ex: phone-in polling: a radio personality will his or her listeners to phone the station to submit their opinions

cluster sample

obtained by dividing the population into groups and selecting all individuals from within a random sample of the groups

systematic sample

obtained by selecting every kth individual from the population. the first individual selected corresponds to a random number between 1 and k does not require a frame and is a useful technique when you cannot obtain a list of the individuals in the population

To estimate the percentage of defects in a recent manufacturing batch, a quality control manager at Microsoft selects every 10th software CD that comes off the assembly line starting with the sixth until she obtains a sample of 30 software CDs. What type of sampling is used?

systematic

random sampling

the process of using chance to select individuals from a population to be included in the sample for the results of a survey to be reliable the characteristics of the individuals in the sample must re representative of the characteristics of the individuals in the population the key to obtaining a sample representative of the population is to let chance or randomness play a role rather than convenience if convenience is used to obtain a sample, the results of the survey are meaningless

To determine customer opinion of their inflight service, Continental Airlines randomly selects 110 flights during a certain week and surveys all passengers on the flights. What type of sampling is used?

Cluster

true or false: when obtaining a stratified sample, the number of the individuals included within the stratum must be equal.

False. Within stratified samples, the number of individuals sampled from each stratum should be proportional to the size of the strata in the population A stratified sample is obtained by separating the population into non overlapping groups called strata and then obtaining a simple random sample from each stratum. The individuals within each stratum should be homogeneous (or similar) in some way. In order for the stratified sample to be representative of the population, the number of individuals sampled from each stratum should be proportional to the size of the strata in the population. For example, if one wanted to take a stratified sample of 100 individuals from a population that is 53% female and 47% male, then 53 females and 47 males should be sampled.

True or false: Inferences based on voluntary response samples are generally not reliable.

True, because it is often the case that the individuals who volunteer do not accurately represent the population

when conducting a cluster sample, it is better to have fewer clusters with more individuals when the clusters are heterogenous? True or False

True, because when the clusters are heterogeneous, they are scaled down versions of the population heterogeneous cluster likely resembles the heterogeneity of the population. each cluster is a scaled-down representation of the overall population

simple random sampling

a sample of size n from a population of size N is obtained through simple random sampling if every possible sample of size n has an equally likely chance of occurring. The sample is then called a simple random sample. the number of individuals in a sample is always less than the number of individuals in the population

sample without replacement

an individual who is selected is removed from the population and cannot be chosen again once an individual is selected, the individual is removed from the possible choices for that sample and cannot be chosen again