Descriptive Statistics

Overview of Data and Key Terminology

  • Data: The facts and figures collected, analyzed, and summarized for presentation and interpretation.

  • Variable: A characteristic or a quantity of interest that can take on different values.

  • Observation: A set of values corresponding to a set of variables.

  • Variation: The difference in a variable measured over observations.

  • Random Variable (Uncertain Variable): A quantity whose values are not known with certainty.

  • Summary Data for Dow Jones Industrial Index Companies:

    • Apple (Symbol: AAPL) | Industry: Technology | Share Price: $195.57 | Volume: 21,060,685

    • American Express (Symbol: AXP) | Industry: Financial | Share Price: $123.16 | Volume: 2,387,770

    • Boeing (Symbol: BA) | Industry: Manufacturing | Share Price: $369.32 | Volume: 3,002,708

    • Caterpillar (Symbol: CAT) | Industry: Manufacturing | Share Price: $133.71 | Volume: 3,747,782

    • Cisco Systems (Symbol: CSCO) | Industry: Technology | Share Price: $56.08 | Volume: 25,533,426

    • Chevron Corporation (Symbol: CVX) | Industry: Chemical, Oil, and Gas | Share Price: $123.64 | Volume: 4,705,879

    • Disney (Symbol: DIS) | Industry: Entertainment | Share Price: $139.94 | Volume: 14,670,995

Data Classification and Data Types

  • Population: All elements of interest in a study.

  • Sample: A subset of the population.

  • Random Sampling: A sampling method used to gather a representative sample of population data.

  • Quantitative Data: Data on which numeric and arithmetic operations, such as addition, subtraction, multiplication, and division, can be performed.

  • Categorical Data: Data on which arithmetic operations cannot be performed.

  • Cross-Sectional Data: Data collected from several entities at the same, or approximately the same, point in time.

  • Time Series Data: Data collected over several time periods.

    • Graphs of time series data are frequently found in business and economic publications.

    • These graphs help analysts understand what happened in the past, identify trends over time, and project future levels for the time series.

    • Example: Dow Jones Index Values since 2006 show historical values fluctuating between 5,000 and 22,000 across the timeframe from 2006 to 2017.

Data Sources and Observational Methods

  • Experimental Study:

    • A variable of interest is first identified.

    • One or more other variables are identified and controlled or manipulated so that data can be obtained regarding how they influence the variable of interest.

  • Nonexperimental Study (Observational Study):

    • Makes no attempt to control or manipulate the variables of interest.

    • A survey is the most common type of observational study.

Modifying Data in Excel

  • Top 20 Top-Selling Automobiles Data Set (February 2019 vs. February 2018 Sales and Percentage Change):

    • Rank 1: Toyota Corolla | Feb 2019 Sales: 29,016 | Feb 2018 Sales: 25,021 | Percent Change: 16.0%16.0\% ($$15.97\%