Sampling for Drug Use Indicators Study

1. Sampling for Drug Use Indicators Study

2. Sampling for Drug Use Indicators Study: Objectives • Describe the principles upon which sampling is based. • Identify and describe different sampling methods. • Select a sample of health facilities from a list of such facilities using at least two different methods. • Compare the the results of the methods. • Instruct others how to sample for drug use studies. Sampling to Study Drug Use

3. What is Sampling? • Sampling is a process by which we study a small part of a population to make judgements about the entire population. Sampling to Study Drug Use

4. Sampling involves selecting a number of units from a defined population. Sampling to Study Drug Use

5. Sampling Definitions • Sampling Unit- The thing which is sampled, for example, a person, a clinical episode, or a health facility • Study Population- All the sampling units which could possible be included in the sample • Sampling Frame- A list of all the available sampling units in the study population Sampling to Study Drug Use

6. A Representative Sample A representative sample has all the important characteristics of the studypopulation from which it isdrawn. Sampling to Study Drug Use

7. Sampling Methods • Two categories of sampling methods:- Non probability sampling - Probability sampling Sampling to Study Drug Use

8. Non Probability Sampling Methods • Convenience Sampling- study units available at the time of data collection are selected for the sample • Quota Sampling- different categories of sample units are included until a certain number has been reached in each category Sampling to Study Drug Use

9. Probability Sampling Methods • Simple Random Sampling • Systematic Sampling • Stratified Sampling • Cluster Sampling • Multistage Sampling Sampling to Study Drug Use

10. Simple Random Sampling • Used in situations where the number of sampling units is relatively small • Process:- Identify all possible units available for sampling- Decide on the size of the sample- Choose units by a lottery method Sampling to Study Drug Use

11. Systematic Sampling WithEqual Probability • Numbered list of all possible units. • # units  desired sample size = sampling interval. • For example, to select 20 health centers from a list of 46, the sampling interval is 46/20 = 2.3 • Random # x sampling interval = random start. • For example, if the random number is 0.183 calculate 0.183 × 2.3 = 0.421, which rounds upward to 1 • Round number up to choose sample unit. • Add sampling interval to random start for subsequent units. • For example, 0.421 + 2.3 = 2.721 or Facility 3 2.721 + 2.3 = 5.021 or Facility 6 5.021 + 2.3 = 7.321 or Facility 8 and so forth. Sampling to Study Drug Use

12. Systematic Sampling WithProbability Proportional To Size • List where the units are sorted in decreasing order by some measure of size (like population or number of visits) • Calculate the cumulative total. • Cumulative total  sample size = sampling interval. • Random # x sampling interval = random start. • Choose first unit with cumulative total result. • Add sampling interval to previous total for subsequent units. Sampling to Study Drug Use

13. Stratified Sampling • Used when the sampling frame contains clearly different categories (strata). • For example: • Urban and rural facilities • Facilities with and without doctors • Government and mission facilities • Process:-Organize the list of sampling units by stratum- Select units within each stratum using a random method (simple random sampling or systematic sampling) Sampling to Study Drug Use

14. Cluster Sampling • Used when for logistic reasons it is easier to select sample units in groups • Process- Select a cluster of sample units- • Example: health center with multiple prescribers • Include the entire cluster or select a sub- sample • OR -Select a random sample unit to start each cluster (a house, a patient, etc.)- Include neighboring sample units until a certain cluster size is reached Sampling to Study Drug Use

15. Multistage Sampling • Randomly select primary sampling units at the first stage: • specific communities • specific health facilities • Within the primary sampling units, randomly select the final sampling units at the second stage: • drug use encounters • patients • households • Sometimes in complex samples, additional stages are needed Sampling to Study Drug Use

16. Sample Size • The optimal sample size is often a compromise between what is statistically Desirable and what is practically Feasible. In general, a minimum sample size is 30. Sampling to Study Drug Use

17. Sample size 50 100 200 500 1000 Range of Confidence 36 - 64% 40 - 60% 43 - 57 % 45 - 55 % 47 - 53 % Sample Size Confidence Intervals If the real figure is 50% Sampling to Study Drug Use

18. Conclusion • Principles of sampling should be understood by everyone involved in drug use studies. • Eumerators and supervisors shouldunderstand that any facility, anyprescription, or any patient should have a chance to be included. • Make every effort to avoid bias in selecting units for study. Sampling to Study Drug Use

19. Activity One Sample Selection In this exercise, groups will use the different sampling methods on a real data set to select a sample. The results of the different sampling methods will be compared. Sampling to Study Drug Use