Statistics

Statistics

1. Measurement Scales

   • Nominal
     • Has: -Identity
   • Ordinal
     • Has: -Identity -Magnitude
   • Interval
     • Has: -identity -Magnitude -Equal intervals
   • Ratio
     • Has: -Identity -Magnitude -Equal intervals -Absolute zero

2. Statistics basic concepts

   • Type of variable
     • Qualitative
       • no countable data
     • Quantitative
       • can be countable
       • Discrete
         • is counted
       • Continuous
         • is measured
   • Population
     • Parameter
   • Sample
     • Statistic

3. Visual displays of data

   • Frecuency Distribution
     • Frecuency
       • # of times an event happens
     • Relative frecuency
       • percentage that represents each datum
     • Grouped frecuency distribution
       • -Cada dato pertenece a una clase -Todas las clases del mismo ancho -Mutuamente excluyentes
   • Displays
     • Histogram
     • Stem & leaf
     • Bar graphs
     • Circle graphs
     • Line graphs

4. Measures of central tendency

   • Mean
     • Σxi ------ n
   • Weghted mean
     • Σxf ------- Σf
   • Mode
     • Most repeated datum
   • Median
     • -Not so sensitive to extreme values. -Has the half of the number below and half above.
     • Position
       • (n+1)/2
       • (Σf+1)/2

5. Measures of dispersion

   • Range
     • R = V - v
   • Chevyshev's Theorem
     • 1-(1/k^2)
   • Coefficient of variation
     • 100s ------ mean
   • Standard Deviation
     • 1. Calcular media 2. Calcular desviación media 3. Elevar al cuadrado 4. Sumar desviaciones 5.Dividir entre n-1 (o n) 6. Aplicar raíz

6. Measures of position

   • Percentil
     • Each 100th part
   • Decil
     • Each 10th part
   • Quadrantal
     • Each 4th part divided by Q1, Q2 &Q3
     • Box plot

7. Sampling Methods

   • Probability samples
     • Each element has a zero probability of appearing in the sample
     • Simple random sampling
       • All the elements have the same probaility to be choosen
     • Stratified sampling
       • Population divided into groups based on a characteristic
     • Cluster sampling
       • Population divided into groups formed randomly
     • Multistage sampling
       • Use a combination of different methods
     • Systematic random sampling
       • Create a list of elements of the population and choose one element every k number of elements
   • Non-probability samples
     • The probability of an element of no appearing in the sample is unknown.
     • Voluntary
       • Self-selected
     • Convenience
       • People who are easy to reach

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