Statistics

Statistics

1. Basic concepts (for examples)

   • Population
   • Sample
   • Identified variable
   • Type of variable
   • Data
   • Parameter
   • Statistics

2. Measurement scales

   • Nominal: Measurement property. Descriptive, no inherent numerical value. E.g. Gender.
   • Ordinal: Identity and magnitude properties. Values have unique valus and an ordered relation between them. E.g. Results from competition.
   • Interval: Identity, magnitude and equal intervals properties. Know wether different values are bigger or smaller and how much different they are. E.g. Fahrenheit 50°-60°=40°-50°
   • Ratio: Identity, magnitude, equal intervals and minimum value of 0 properties. E.g. Weight of an object. (All properties together.)

3. Sampling methods

   • Non-probability
     • Voluntary: People self-select for the survey. (Web surveys)
     • Convenience: Made up of people easy to reach.
     • Quota: A defined sample chosen out form a sub-group by the surveyer.
   • Probability
     • Systematic: Every possible sample of n elements is not equally likely.
     • Cluster: Clusters are groups randomly created where only individuals within are survyed.
     • Stratified: Population is divided in strata which are the characteristics the surveyer looks for.
     • Simple random:With population N and sample n, all n objects are equally likely to occur. (Lottery)

4. Visual displays of data

   • Displays:
     • Line graphs
     • Circle graphs
     • Bar graphs
     • Stem and leaf
     • Histogram
   • Frecuency distribution
     • Frequency: number of times corresponding item occurs in data set.
     • Fraction ot percentage of the data set represented by the item.
     • Grouped frequency distribution: Make each data item will fit only into one class; make all classes the same width; Make sure classes do not overlap; use from 5-12 classes.

5. Measures of central tendency

   • Median: (n+1)/2, ordered from least to most.
   • Mode: Value that occurs most often
   • Mean: sum of all items between the number of these.
   • Wieghted mean

6. Measures of dispersions

   • Standar deviation
   • Range: Greatest value-least value
   • Chebyshev's theorem
   • Coefficient of variation

7. Measures of position

   • Z-score: Standar score
   • Decile: D1, D2...D1O Quartile: Q1, Q2, Q3, Q4 Percentile: 1% to 100%
   • Box plot

8. Luis David Alcalá Díaz A01400383

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