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MED 106- RESEARCH METHODS AND ESSENTIAL MEDICAL STATISTICS > 3. FREQUENCY DISTRIBUTIONS > Flashcards

3. FREQUENCY DISTRIBUTIONS Flashcards

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USMLE® Step 1 flashcards
1
Q
  1. What do we look at when describing the distribution of a numeric value?
A
  • we look for the overall pattern
  • we look for striking deviations from the pattern
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2
Q
  1. What 3 characteristics do we describe a histogram by?
A
  • its shape
  • its centre
  • its spread
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3
Q
  1. What kind of Distribution is this?
A
  • it is symmetric
  • it is normal (Gaussian)
  • it is unimodal
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4
Q
  1. What kind of Distribution is this?
A
  • it is skewed
  • it is unimodal
  • it is not symmetric
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5
Q
  1. What kind of Distribution is this?
A
  • this is a Bimodal Distribution
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6
Q
  1. What does Unimodal mean?
A
  • this means one peak
  • this means that there is a single most common value
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7
Q
  1. What does Bimodal mean?
A
  • this means two peaks
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8
Q
  1. What does Multimodal mean?
A
  • this means multiple peaks
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9
Q
  1. When is a distribution said to be Symmetrical?
A
  • this is also known as a Normal Distribution
  • this happens if the right and left sides of the Histogram
    are approximately mirrored images of each other
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10
Q
  1. What two other names can we call a Symmetrical distribution?
A
  • a Bell Curve
  • a Gaussian Distribution
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11
Q
  1. What is a Positively Skewed Distribution?
A
  • this is when a distribution is skewed to the right
  • the right side of the Histogram extends much further
    out than the left side
  • this means that the distribution is said to have a right
    tail
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12
Q
  1. What is a Negatively Skewed Distribution?
A
  • this is when a distribution is skewed to the left
  • the left side of the histogram extends much further out
    than the right side
  • this means that the distribution is said to have a left
    tail
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13
Q
  1. What can be said about the Mode across these three different kinds of distributions?
A
  • the mode is unchanged
  • the graph shape has no effect on it
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14
Q
  1. What can be said about the Median and the Mean across these three different kinds of distributions?
A
  • the Median and the Mean are pulled towards the
    direction of the skew
  • the results of the Median would be more reliable than
    the results of the mean for this situation
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15
Q
  1. What are the Mean and the Median for this Normal Distribution?
A
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16
Q
  1. What are the Mean and the Median for this Positively Skewed Distribution?
A
  • the Mean is pulled towards the skew more severely
    than the Median
  • the Median reflected the data better
17
Q
  1. What parameters do you use when the data is skewed?
A
  • you use the Median
  • you use the IQR
  • DO NOT USE the standard deviation
  • DO NOT USE the mean
18
Q
  1. What is an Outlier?
A
  • Outliers are observations that lie outside the overall
    pattern of a distribution
  • make sure to always look for outliers and interpret
    them
19
Q
  1. What happens to the original mean when we have an outlier?
A
  • the mean is changed dramatically
  • it is pulled towards the direction of the skew
20
Q
  1. What happens to the original median when we have an outlier?
A
  • the median remains largely unchanged
21
Q
  1. Provide descriptions for Labels 1-4.
A
  1. Skewed Right
  2. Skewed Left
  3. Normally Distributed Variable
  4. Skewed Variable
22
Q
  1. Which methods should be use to check the distribution of numeric variables?
A
  • a histogram
  • a box-plot
23
Q
  1. For which kind of distributions should we only use Box-plots and histograms?
A
  • for normal distributions
  • this is because the mean is affected by skewness and
    outliers
  • it should only be used for variables that do not have
    outliers
24
Q
  1. Do outliers always affect the mean?
A
  • NO
  • a few outliers will not affect the mean of a very large
    sample
25
Q
  1. Does skewness always effect the mean?
A
  • YES
  • no matter how small the sample is
26
Q
  1. What affects the Standard Deviation?
A
  • skewness
  • outliers
27
Q
  1. In which situations should we make use of the Standard Deviation?
A
  • it should only be used when the variable is normally
    distributed
  • it should only be used when there are no outliers
    present
28
Q
  1. What is the only parameter that is infrequently used in Scientific Research?
A
  • mode
29
Q
  1. What percentage of values falls into a sample contained in a range that is one standard deviation from the mean?
A
  • 68%

NB:
- this applies explicitly for distributions that are perfectly
normal

30
Q
  1. What percentage of values falls into a sample contained in a range that is two standard deviations from the mean?
A
  • 95%

NB:
- this applies explicitly for distributions that are perfectly
normal

MED 106- RESEARCH METHODS AND ESSENTIAL MEDICAL STATISTICS (43 decks)

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