Question

1. which of the following is not true for stratified random sampling? a) an srs is taken from each stratum. b) individuals within each stratum are homogenous based on some characteristic. c) every possible sample of size n from the population has an equal chance of being selected. d) individuals cannot belong to multiple strata. e) strata are clearly defined prior to sampling. 7. a research company is interested in estimating the mean number of minutes people spend on social media apps. a random sample will be selected from each of four strata: children (12 - 17 years old), young adults (18 - 30 years old), middle - aged adults (31 - 45 years old), and older adults (above 45 years old). selected individuals will be asked the number of minutes they spend on social media apps on a typical day. why is stratification used in this situation? a) to remove bias when estimating the proportion of individuals in each age range b) to remove bias when estimating the mean time spent on social media apps c) to reduce bias when estimating the mean time spent on social media apps d) to decrease variability in the estimate of the proportion of individuals in each age range e) to decrease variability in the estimate of the mean time spent on social media apps

Explanation:

For question 6, in stratified random sampling, an SRS is taken from each stratum (A is true), individuals within a stratum are homogenous (B is true), strata are clearly defined (E is true), and individuals cannot belong to multiple strata (D is true). But in stratified random sampling, not every possible sample of size n from the population has an equal chance of being selected as samples are drawn from each stratum separately. For question 7, stratification is used to decrease variability in the estimate of the parameter of interest. Here the parameter of interest is the mean time spent on social - media apps, and stratifying by age groups helps to decrease the variability in the estimate of this mean.

Answer:

1. C
2. E