Population and Sampling Methods PDF

# Population and Sampling ## Population Diana - The collection of all individuals that share characteristics in a study. ## Stratum - Groups formed within a population. ## Sample - A representative subset of the population selected to gather information. ### Sampling Methods #### Probabilistic...

# Population and Sampling ## Population Diana - The collection of all individuals that share characteristics in a study. ## Stratum - Groups formed within a population. ## Sample - A representative subset of the population selected to gather information. ### Sampling Methods #### Probabilistic Methods - All individuals have an equal probability of being selected. - Types include: - Simple random - Systematic - Stratified - Cluster - Multistage #### Non-Probabilistic Methods - The probability of an individual being part of the sample is unknown and variable. - There is no random selection. ## Measures of Position - These statistics describe the relative position of a data point within a set. - Examples include: - **Quartiles**: Divide a set into four equal parts. - **Deciles**: Divide a set into ten equal parts. - **Percentiles**: Divide a set into 100 equal parts. ## Calculating Sample Size - The formula is: n = 2.VN (minus) - For example, if there are 225 individuals, 30 individuals would be selected. ## Measures of Central Tendency - The measures of central tendency are used to find the central value within a given set. - Examples include: - **Arithmetic mean** - **Geometric mean** - **Harmonic mean** - **Median** - **Mode** ## Classification Criteria ### According to the Unit of Analysis - **Ecological**: Groups of individuals are the unit of analysis, whether for experimental or observational studies. - **Individual**: The researcher collects individual data for their studies. ### According to the Type of Final Results - **Intervention**: The researcher intervenes. - **Observational**: The researcher only observes. ### According to the Period of Study - **Transversal**: Information is gathered at the same time for each individual within a certain period. - **Longitudinal**: Information is gathered at different moments within a given time period. ### According to the Temporal Sequence of Data Collection - **Retrospective**: The researcher looks for the past causes of an already occurred event. - **Prospective**: The researcher studies possible causes and their effects. ## Specificity - The probability of correctly identifying an individual as healthy. - Formula: E = d / (b + d) - d = true negatives - b = false positives ## Negative Predictive Value - The probability that a negative test truly indicates that the individual is healthy. - Formula: VPN = d / (c + d) - c = false negatives - d = true negatives ## Types of Studies ### Cross-Sectional Studies - These studies are observational and descriptive. - They gather information about health status and exposure at the same time point. ### Cohort Studies - These are observational and analytical. - They typically begin with a healthy population and follow participants over time. ### Ecological Studies - The unit of analysis is a population or group of individuals. - They often use secondary data and are used to generate hypotheses. ## Selection of Diagnostic Tests ### Technical Criteria - **Sensitivity**: The ability of a test to correctly identify individuals with a disease. - **Specificity**: The ability of a test to correctly identify individuals without a disease. - **Youden's Index**: (Sensitivity + Specificity) -1 - **Reliability**: The consistency of a test. - **Predictive Values**: The probability of a test result being accurate. ### Economic Criteria - **Cost**: The financial cost of the test. - **Impact of disease**: The consequences of the disease. ### Logistic Criteria - **Time to results**: The time it takes to get test results. - **Processing capacity**: The ability to process large numbers of tests. - **Technical complexity**: The difficulty of performing the test. - **Automation**: The possibility of automating the test. - **Side effects**: Any adverse effects of the test.