![]() ![]() This just creates an “empty” variable with no values (in R, NA is what is used for a missing value). This can be done by creating a new variable in the data frame called N. This suggests that stratification for sampling from this population may be worthwhile, particularly if optimal or Neyman allocation is used.īefore specifying the design it is necessary to include the stratum sizes (i.e., \(N_1\), \(N_2\), \(N_3\), and \(N_4\)) in the data frame. ![]() Interestingly the distribution of the number of holts is very similar for the cliffs, agricultural, and non-peat sections, but markedly different for the peat sections. boxplot(holts ~ habitat, data = otters, ylab = "Number of Holts", xlab = "Habitat") It might be interesting to visualize the survey data. otters$habitat <- factor(otters$habitat, labels = c("cliffs", "agricultural", This can be done by changing habitat into a factor using the factor function and assigning labels to the strata. Although not necessary for the analysis, it would be helpful to have the stratum names be more descriptive. Here are the first six observations: head(otters) section habitat holtsĮach observation includes the section number, the type of habitat, and the number of holts. If you have not done so already you will need to install this package using install.packages("SDaA"). ![]() The data are available in the SDaA package. The sample featured here was collected using stratified random sampling. 2 The coastline was divided into 237 5km habitable sections, with each section classified as one of four types: cliffs over 10m (89 sections), agricultural (61 sections), peat (40 sections), and non-peat (47 sections). Homework grades of sports participants.Kruuk et al. (1990) used a stratified random sampling design to estimate the number of otter ( Lutra lutra) dens or holts along a 1400km coastline of the Shetland Islands. The number students in your school with access to the internet.ġ5. The average height of college basketball players.ġ3. automobiles compared to vehicle weight.ġ2. What percent of the sample is made up of cats?įor questions 11-15, decide whether a stratified sample is warranted and why.ġ1. What would the total population be if there were no horses?ġ0. ![]() Are there more than 1000 pot-bellied pigs in the population?ĩ. What percentage of the population is represented by dogs?Ĩ. How many horses are there in the entire population?ħ. Assume the total population of pets is 6474.Ħ. Should you have more than 15% of your sample represented by trucks?įor questions 6-10, assume your stratified sample consists of 29 cats, 62 small dogs, 48 large dogs, 19 birds, 37 pot-bellied pigs, and 55 horses. Is 10 R.V.’s a good number for your sample?ĥ. How many subcompacts should you have in your sample?Ĥ. How many motorcycles should you have in your sample?ģ. What percentage of the population is represented by sedans?Ģ. Look to the end of the lesson for the answer.įor questions 1-5, assume you intend to create a stratified sample of 250 from a population of 920 trucks, 1540 subcompact cars, 1320 sedans, 450 motorcycles, 110 R.V.’s, 550 luxury cars, and 780 sports cars.ġ. How could you make sure a random sample of college students would have members of each age range? You might divide the students up by age ranges such as: Under 18, 18 – 21, 21 – 25, 25 – 35, and 35 and over. Suppose you wanted to find out if age influences the choice of classes for students at a particular university.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |