# Essay on Stats: Sampling and Population

Submitted By lucy629
Words: 2534
Pages: 11

CHAPTER 1
Statistics: art of collecting, classifying, interpreting, and reporting numerical information related to a particular subject.
Statistic: a numerical fact of interest in some context.
Population: the total set of objects or measurements that are of interest to a decision maker
2 SETS OF TECHNIQUES IN STATS:
---DESCRIPTIVE: focused on summarizing and presenting information. Data set: the set of all observations for a given project or purpose
---INFERENTIAL: designed for making estimates or inferences about the characteristics of a population based on the info found in one or more SAMPLE: representative subsets of the population INFINITE POPULATION: not realistically possible to count every single member of population ( cars in the world)
FINITE POPULATION: possible and realistic to count every member (weight/ gender of member)
CENSUS: a set of observations taken from every member of population
PARAMETER: a value for summarizing the measurements of a quantifiable feature of the population
SAMPLE STATISTIC: if the corresponding feature is measured in the sample
ESTIMATE= INFER
WHY USE SAMPLES?
1) Time constraints ( decision deadlines, trends, seasonality)
2) Cost constraints
3) Unknown population size
4) Destructive tests
5) Greater accuracy of some samples
REPRESENTATIVE SAMPLE: sample should be representative of population ( half balls blue, half balls green , even though the size of the balls are different in the big box, the small box has similarity to size and color)
DATA: sets of numeric or nonnumeric facts the represent records of observations … single observation is called DATUM…set of all observations for a given project or purpose is called DATA SET
CONSTANT: an observed characteristic whose value does not change over time or in a different experiment (like the circumference to its diameter)
VARIABLE: observed characteristic that can change from observation to observation (number of strikeouts in a game) RANDOM VARIABLE: something that happens by chance or is unplanned (cannot be known in advance) QUALITATIVE RANDOM VARIABLE: not a result of a numerical value, one observes a trait or characteristic that can be classified into a number of categories (NDP, GREEN PARTY, LIBERALS, NONE) QUANTITATIVE RANDOM VARAIBLE: random variable that takes values that varies in magnitude (discrete or continuous) DISCRETE RANDOM VARIABLE: restraints on values (cars can’t be 3.75 either 3 or 4) CONTINUOUS RANDOM VARIABLE: any value over a particular range of values (height)
DATA
VARIABLES CONSTANTS
RANDOM V NONrandom V
Qualitative RV Quantitative RV: Discrete & Continuous

LEVELS OF MEASUREMENT: (highest level to lowest level, contain more info to contain less info)
Quantitative: RATIO, INTERVAL Qualitative: ORDINAL, NOMINAL
NOMINAL: Ford, Chrysler, GM