lect 2 desctriptive and inferencial statts and CI Flashcards Preview

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Flashcards in lect 2 desctriptive and inferencial statts and CI Deck (17)
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1

what are descriptive statistics

statistics used by researchers to report on samples.

summarize information to speed up and simplify the comprehension of a population’s  characteristics.

2

how do descriptive techniqes organize data

tables

  • freq distributiona
  • relative frequency distrubutiona

graphs 

  • bar chart
  • histogram
  • boxplot

3

how do descriptive stats summarize data

central tendency/ mid sample value (location)

  • Mean

  • Median

  • Mode

variation summary diff w/in a groupm(spread)

  • Range

  • Interquartile range

  • Variance

  • Standard deviation

4

what is the mean 

average

add up values for each case and divide by total number of cases

5

describe the median 

  • The middle value when a variable’s values are ranked in order
  • point that divides a distribution into two equal halves
  • if data are listed in order, point at which 50% of the cases are above and 50% below it

  • The 50th percentile

6

describe the mode 

  • the most common data point 
  • if all values are unique then there isnt one 
  • is not always at the centre of distribution
  • can be multiple

7

define the spread

the Variation of the recorded values on a variable

  • larger spread has cases further from mean
  • smaller spread has individual cases to the mean

8

describe the range 

distance, between the lowest and highest values of a variable.

 

highest value- lowest value.

9

describe Standard deviation

  • how much the members of a group differ from the mean value for the group.
  • larger deviation = increased variation from mean
  • equal to 0, only when all values are the same ( constant and not a “variable”).

 

10

what happens to the mean When a constant is added to every observation

new sample mean is equal to original mean plus the constant.

11

what happens to the standard deviation when a constant is added to every observation,

standard deviation is unaffected.

12

what happens to the sample mean when every observation is multiplied by the same constant,

new sample mean is equal to original mean multiplied by the constant.

13

what happens to the standard deviation when every observation is multiplied by the same constant,

new sample standard deviation is equal to original standard deviation multiplied by the magnitude of the constant.

14

what is the normal distrubution 

MEAN and SD are appropriate for histogram summary

bell shaped curve where the mean is at it's peak 

histogram: graphical display of data using bars of different heights

15

what are the three rules of sigma when data has an approx normal distribution

approximately 68% of the data lie within one SD of
the mean

approximately 95% of the data lie within two SDs of
the mean

approximately 99.7% of the data lie within three SDs
of the mean

16

what is the difference betw/ standard error of a mean & standard deviation

when the mean estimates individual values standard deviation = the degree of uncertainty by which the mean estimates individual values  

 

when the mean estimates the population mean standard error of mean = the degree of uncerntainty with which the mean estimates the population mean 

17

what is the confidence interval of the mean

a range of values around the mean where we expect the "true" population mean is located.

 

µ=x+/-1.96xSEM

 

example 

  • X = 9.5 years; SD = 2.8 years

    SEM = 0.5 years

    95% level of confidence => Z = 1.96

    µ = 9.5 ± (1.96 x 0.5) = 9.5 ± 1 years

    95% CI for µ is (8.5; 10.5 years)