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Statistical Methods in Biology (Lecture) Statistics- is a branch of science which deals with the collection, presentation and analysis, an interpretation of quantitative data. Collection of Data Population - the total units under investigation - set of data that consists of all hypothetically possible observation of a certain phenomenon. *Experimental Design (Definite) A. B. Sample - part of the population - set of data that contains only a part of the total observations. C. Census - method of collecting data of a population General Methods of Sampling A. Probability Sampling - all elements are given the chance to be selected as a sample. B. Non-probability Sampling - not all elements are given the chance to be selected as a sample. Common methods of drawing probability samples A. Simple Random Sampling B. Systematic Sampling - makes a constant Interval. - needs a frame or list - compute for the sampling interval - pick the first sample at random 1st sample =7 2nd sample = 7+10 3rd sample = 7 + 2 (10) 4th sample = 7 + 3 (10) 50th sample = 7 + 49 (10) = 17 = 27 = 37 = 497 D. Sampling (Sample Survey) - method of collecting data from samples E. Parameter - value taken from population data (Result) F. 1. 2. 3. 4. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Statistic - value taken from a sample data (Estimator of a parameter) Advantages of Sampling over Census Reduced Cost Greater Speed Greater Scope Greater Accuracy Principal Steps in a Sample Survey Formulate the objective of the survey Define the population to be sampled Identify the data to be connected Specify the degree of precision desired (95% or 99%). Choose the instrument to be used Construct a list of sampling units or frame Select for an appropriate size of sample. Conduct a pre-test Organization of field work Summary and analysis of data Record information gained for future use 01 / 22 / 19 Use SI = 13 1st sample = 11 2nd sample = 11 + 13 = 24 5th sample = 11 + 4 (13) = 64 last sample = 11 + 99 (13) =1298 - non-probability sampling since not all elements were given the chance to be selected as a sample. - identify the effect - increase sample size only Use SI = 13 1st sample 2nd sample last sample 99th sample 98th sample *kulang 2 = 12 = 12 +13 = 12 + 99 (13) = 12 + 98 (13) = 12 + 97 (13) = 25 = 1299 = 1286 = 1273 C. Stratified Sampling - pick sample from every (barangay); homogenous groups 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 *equal (n=90; probability proportionate to size D. Cluster Sampling - heterogenous (pili la o usa la); iba-iba it population or sample size 1 2 3 4 5 6 7 8 9 Common Non-Probability Sampling 1. Purposive Sampling 2. Convenience Sampling 3. Quota Sampling 01 / 25 / 19