Biology Statistics Flashcards
(6 cards)
Standard deviation ~
- What it means
- Steps
- What results show
- A measure of VARIATION
- Measures the SPREAD of data from the MEAN.
- Calculate the MEAN of all the values (x)
- SUBTRACT the mean from each value of x (x-xbar)
- SQUARE each value of x-xbar
- ADD all these values ( sum of (x-xbar)^2
- DIVIDE this by the total number of values MINUS 1
- SQUARE ROOT value
What do standard deviation values indicate?
LOW Standard deviation:
- More tightly clustered the values are around the mean
- Less variation in the data
- Greater reliability
HIGH Standard deviation:
- Values have a larger range from the mean
- More variation in the data
- Less reliability
Student t-test
- Used to COMPARE two means
- Allows us to measure whether the difference between two means is SIGNIFICANT
- Have to give a NULL HYPOTHESIS ~ that there is no significant difference
- The t-test will then show whether we reject or accept the hypothesis
Deciding whether the difference between the two means are significant ( Student t-test)
DEGREES OF FREEDOM ~ the number of values in a statistical calculation that are free to vary. Calculated:
sample size (n1+n2) - number of data sets
If our t-value is:
HIGHER than 5% significance level = significant
LOWER than 5% significance level = NOT significant
Correlation Coefficient & Spearman’s Rank
- What it measures
- Steps to calculate
- Used to consider the relationships between two sets of data
- Measures whether two sets of data are
correlated or not - State a NULL HYPOTHESIS
- RANK the values from highest to lowest for the two sets of data
- Calculate the DIFFERENCE between the two ranks (R1-R2)
- SQUARE each of these values ( D^2)
- ADD up all the D^2 values
- PLUG values into equation
Deciding whether there is a significant correlation between the two sets of data.
(Spearman’s Rank)
- You will be given a table with the number of pairs of measurements with a CRTICAL VALUE
Compared to the critical value, if our calculated value is:
LOWER = NO significant correlation
HIGHER = Significant correlation
NEGATIVE value = NEGATIVE correlation
POSITIVE value = POSITIVE correlation
