Statistical Analysis of Data Tutorial

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Statistical Analysis of DataTutorial

• Biology Labs
• 1406/1408
• Dr. Orr

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Mean

• This is an average of a group of measurements.
• How do I calculate mean?
• Add all values and divide by total number of
  values.
• Example values- 40, 38, 22, 20, 30
• Mean 40382240 30 divided by 5 30

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Median

• The value that is in the middle of a group of
  measurements.
• How do I calculate median?
• Using previous example
• Example values- 40, 38, 22, 20, 30
• Rearrange from low to high- 20, 22, 30, 38, 40
• Median middle value 30

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Range

• The difference between the smallest and the
  largest measurements.
• How do I calculate range?
• Using previous example
• Example values- 40, 38, 22, 20, 30
• Subtract smallest value, 20, from largest value,
  40
• Range 40 20 20

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Deviation

• Measures how the measurements vary from the mean
  ( or -). In other words, what is the difference
  between an actual measurements and the mean, or
  average, of the sample?
• How do I calculate a deviation?
• Using previous example
• Example values- 40, 38, 22, 20, 30
• We determined the mean to be 30. The deviation
  for the value 38 would be 8. This value is 8
  more than the mean.

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Variance

• This measures how much difference, or variation,
  there is between the values you have obtained.
  The smaller the variance, the closer the values
  will be to the mean. Likewise, the larger the
  variance, the farther the values will be from the
  mean.
• How do I calculate variance? Calculate the sum
  of the squared deviations divided by the number
  of values minus one.
• Using previous example
• Example values- 40, 38, 22, 20, 30
• (102 82 -82 -102 02) 82
• 5 - 1

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Standard Deviation

• Standard deviation gives you an idea of the
  widely spread your values are about the mean.
• How do I calculate Standard Deviation? Calculate
  the square root of the variance.
• Using previous example
• Example values- 40, 38, 22, 20, 30
• The variance equaled 82, to determine S.
  Deviation take the square root of 82 9.06

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Null Hypothesis vs. Research (alternate)
Hypothesis

• The null Hypothesis states that there are no
  differences (null effect) between conditions
  being compared.
• A research (also known as alternate) hypothesis
  is the hypothesis being tested that is that
  there is a difference between conditions being
  compared.

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P-value

• Simply stated, this tells us how probable it is
  that we would see this statistic if the null
  hypothesis is true.
• We look for p values of less that .05 before we
  reject the null hypothesis BECAUSE this indicates
  that there is less than a 5 chance that we would
  see the given values if the null hypothesis is
  true.
• At p values of less than .05, we say that chance
  is slim enough to reject the null hypothesis.
  If a p value is greater than .05, then we do not
  reject the null hypothesis. In this instance,
  chances are greater than 5 that we would see
  these values if the null hypothesis is true.