Populations and Samples

Learn population, sample.

Lesson 2 of 32 parts Practice Flashcards

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Population

Objective: Explain population, apply the stated method, and check its conditions.

The population is the full group about which a study seeks conclusions. A parameter describes that population. Define its membership clearly before choosing a sample; a large sample from a different target group does not answer the intended population question. Specify the target group before assessing sample relevance.

Formulas

Population parameter: a numerical summary of the target group

Worked examples

Try itA school has 700 students. A random survey selects 42 of them. What is the population size?Show answer

Step 1: The population is the full group the study targets. Step 2: The full school has 700 students; the sample has 42. Step 3: The population size is 700.

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Population

Objective: Explain population, apply the stated method, and check its conditions.

Formulas

Population parameter: a numerical summary of the target group

Worked examples

Try itA school has 700 students. A random survey selects 42 of them. What is the population size?Show answer

Step 1: The population is the full group the study targets. Step 2: The full school has 700 students; the sample has 42. Step 3: The population size is 700.

Sample

Objective: Explain sample, apply the stated method, and check its conditions.

A sample is the subset observed or selected from a population. A statistic summarizes that sample and estimates a population parameter only under a defensible sampling design. Sample size is the number of observational units, not the number of variables measured per unit. Representativeness is a design issue, not guaranteed by a large n.

Formulas

n = number of sampled observational units

Worked examples

Try itA synthetic school with 700 students surveys 42 selected students. Find the sample size.Show answer

Step 1: The sample consists of units actually selected for the study. Step 2: Count the 42 surveyed students. Step 3: The sample size is 42, not 700.

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