Transcript SAMPLING
Sampling Randomization Stratification Proportional Clusters Systematic Purposive Randomization 1. Specify the population. 2. Determine sample size. 3. List all members of the population. 4. Assign all individuals on the list a consecutive number from zero to the required number. 5. Select an arbitrary number in the table of random numbers. Randomization 6. For the selected number, look at only the appropriate number of digits. Work your way through through the column until you attain the desired sample size. Stratification 1. Specify the population. 2. Determine the sample size. 3. Identify the variable and subgroups (strata) for which you want to guarantee appropriate representation. 4. Classify all members of the population as members of the identified subgroups. 5. Randomly select an “appropriate” number of individuals from each of the subgroups. Proportional 1. Specify the population. 2. Determine the sample size. 3. Identify the subgroups and subgroups (strata) for which you want to guarantee proportional representation. Proportional 4. Classify all members of the population as members of one of the identified subgroups. 5. Determine the number or ratio of individuals in each subgroup. 6. Randomly select a proportional number Clusters 1. Specify the population. 2. Determine the sample size. 3. Identify and define a logical cluster. 4. List all clusters that comprise the population. 5. Estimate the average number of population members per cluster. Clusters 6. Determine the number of clusters needed by dividing the sample size by the estimated size of the cluster. 7. Randomly select the needed number of of clusters. 8. Include in your study all population members in each cluster. Systematic 1. Specify the population. 2. Determine the sample size. 3. Obtain a list of the population. 4. Determine k by dividing population size by desired sample size. Systematic 5. Start at some random place at the top of the population list. 6. Starting at random point, take every Kth name on the list until the desired sample size is obtained. 7. If the end of the list is reached before the desired sample size is attained, go back to the top of the list. Purposive A type of non-probability sampling characterized by the use of judgment and a deliberate effort to obtain a representative sample. Sample Size Determination 1 Nature of population 2 Type of investigation 3 Degree of precision desired X NP (1 P ) S 2 2 d ( N 1) X P (1 P ) 2 S = required sample size N = population size P = population proportion for table construction has been assumed to be .50 d = degree of accuracy 2 X = table value for chi square Table for Determining Needed Sample Size N 10 25 50 100 150 200 S 10 24 44 80 108 132 N 250 300 400 500 750 1000 S 152 169 196 217 254 278