SYG 4300 02 Social Research Methods Final Review Guide This is a broad list of concepts relevant to the final exam I encourage you to know concepts examples calculations and interpretations The individual units often individual persons that comprise a sample List of all the sampling units from which the sample is drawn Ex telephone directories tax records driver s license records Sample Elements Sampling Frame Sampling Error Sampling error is the deviation of the selected sample from the true characteristics traits behaviors qualities or figures of the entire population Sampling process error occurs because researchers draw different subjects from the same population but still the subjects have individual differences Ways to eliminate Representativeness o This solution is to eliminate the concept of sample and to test the entire population Subset of a statistical population that accurately reflects the members of the entire population Unbiased indication of what population is like Probability vs Non probability Sampling Methods Non probability sampling Probability of being chosen is unknown o o To satisfy concerns about the sample s representativeness the researcher must explicitly explain how the sample represents the population from which it was drawn o Cheaper but unable to generalize o o Convenience Sample ease of access sample is selected from elements of a population that are Potential for bias easily accessible Probability sampling o Methods for drawing a sample in which the probability of selecting population elements is known The researcher uses random sampling so that the representativeness of the sample characteristics to the known population characteristics can be statistically calculated o Random Sample each subject has a known probability of being selected o Allows application of statistical sampling theory to result to Generalize Test hypothesis Ensure representativeness and precision Systematic Random Sample probability sample Create a sampling frame calculate the sampling interval 1 k choose a random starting place then take every 1 k case For example suppose you want to sample 8 houses from a street of 120 houses 120 8 15 so every 15th house is chosen after a random starting point between 1 and 15 If the random starting point is 11 then the houses selected are 11 26 41 56 71 86 101 and 116 o o Advantages o o Easier to conduct than a simple random sample Spreads the sample more evenly over the population Disadvantages o The system may interact with some hidden pattern in the population e g every third house along the street might always be the middle one of a terrace of three Stratified Random Sample probability sample Create a sampling frame for each of several categories of cases draw a random sample from each category then combine the several samples In the first stage elements are sorted into separate groups called strata according to the selected group characteristics In the second stage elements are randomly sampled from within strata Usually use when a stratum of interest is a small percentage of a population and random processes could miss the stratum by chance Ex you have a population that is 51 female and 49 male o You draw 2 random samples one of all females and one of all males ex for a sample of 1 000 draw 510 randomly from a list of males and 490 from a list of females Final sample will have a 51 to 49 percent sex ratio Ex draw a sample of 200 from 20 000 college students and get information that 2 or 400 are divorced women with children under the age of 5 o There would be 4 such students in a representative sample o In stratified random sample you obtain a list of the 400 such students and randomly select 4 from it Advantages o Captures key population characteristics in the sample o Works well for populations with a variety of attributes Cluster Sample probability sample A random sampling plan in which the population is subdivided into groups called clusters so that there is small variability within clusters and large variability between clusters Then the required information is collected from a simple random sample of the elements within each selected group Advantages o Cheaper Disadvantages o Higher sampling error Availability Sample Convenience sample nonprobability sample A nonprobability sample in which elements are drawn based on their availability to the researcher The person on the street interview conducted by television programs is an example Ex a newspaper that asks readers to clip a questionnaire from the paper and mail it in o Not everyone reads the newspaper has an interest in the topic or will take time to cut it out and mail it Quota Sample nonprobability sample Quota sampling is a non probability sampling technique wherein the assembled sample has the same proportions of individuals as the entire population with respect to known characteristics traits or focused phenomenon o The first step in non probability quota sampling is you first identify relevant categories among the population you are sampling to capture diversity among units e g male and female under age 30 ages 30 60 60 and over etc o Next you determine how many cases to get for each category this is your quota o Then you fix a number of cases in various categories of the sample at the start o The final step ensures that the sample is representative of the entire population It also allows the researcher to study traits and characteristics that are noted for each subgroup Ex you interview the first 5 males under 30 you encounter even if all 5 had just walked out of the campaign headquarters of a political candidate o Nothing prevents you from choosing people who act friendly or who want to be interviewed Ex George Gallup successfully predicted the outcomes of the 1936 1940 and 1944 U S presidential elections o o Major reason was that the quota categories did not accurately represent all geographical areas and In 1948 selected the wrong candidate all people who actually cast a vote o Allows the researcher to sample a subgroup of great interest to the study o Allows researcher to observe relationships between subgroups Advantages Disadvantages o May not always be representative of the population o Traits may be overrepresented Purposive sample nonprobability sample A nonprobability sample in which the researcher selects elements for a specific purpose usually because of the unique characteristics of the elements the judgment of an expert or prior knowledge is used to