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BIOSTATISTICS EXAM 1 (CHAP 1-15) STUDY GUIDE
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BIOSTATISTICS EXAM 1 (CHAP 1-15) STUDY GUIDE
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BIOSTATISTICS EXAM 1 (CHAP 1-15) STUDY GUIDEVariable - Answers- A characteristic that differs or varies between individuals.
Any experimental unit of observation for study.
Variability - Answers- The extent to which measurements/individuals/data points differ.
Variable Types - Answers- Numeric/continuous
Categorical
Variable Types: Numeric/Continuous - Answers- can be any numeric/quantitative value.
e.g. Age (can be made categorical), height, weight, mass, volume.
Variable Type Categorical - Answers- Finite or specific number of categories
e.g. gender: M or F
Why is there variability? (E.g. for strawberries) - Answers- -genetics
-nutrients
-sun exposure
-predators
-chance
-location
Statistical Tests - Answers- Test hypothesis.
Look for effects in the face of variability.
-Inferential statistics (Inferential= drawing conclusions on making inferences about
population based on data from a sample.)
Population - Answers- all individuals you are interested in studying
Sample - Answers- Subset of the population that we actually study.
We can use the sample to estimate the population. There will be the same error in our
estimate.
Example: What is the BMI (Body mass index) of adults in the United States?
Numeric: BMI= kg/m^2 or lb/in^2.
Categorical: Underweight <18.5
Healthy weight: 18.5-24.9
Overweight: 25.0-29.9
Obese>=30
,What would be our population? Why is it not feasible to study? - Answers- Our
population is all the adults in the United States.
It's not feasible because our population is too large, the study is too expensive, too time-
consuming, we would need to take into mind consent (can't force participation), and
usually hard to identify population.
Random Sample - Answers- Ideal sample where everybody in the population has an
equal probability of being chosen. Low bias in selecting the sample.
Method for Random Sample: (Adults in the United States) - Answers- 1) Define
inclusion and exclusion criteria to define population.
2) Determine sample size, n, and population size, N.
(generally the larger the sample size, the better it is)
3) # each of the individuals in the population
4) Use random number table or spss to determine the sample
Advantages of Random Sample - Answers- 1) Low bias, objective in selecting
individuals
2) Could potentially select from earlier population
3) Should be representative of population (in theory/has similar characteristics to the
population).
Disadvantages of a Random Sample - Answers- 1) May not be representative of the
population if n is small
2) Consent
3) Usually can't identify the entire population
Convenient Samples - Answers- Most typical sample in biology. We study individuals
that are convenient to study.
Convenient Samples Advantages - Answers- 1) Convenient
2) Mitigates costs and time consumption
=> make larger, add characteristics of population,
use previous experience and studies as a guide
Convenient Samples Disadvantages - Answers- 1) Not representative
2) Biased (by nature)
3) Volunteer bias: (if human volunteers: could be very different in unknown ways to
those that do not volunteer)
Descriptive statistics - Answers- Numbers that are used to describe or summarize the
data.
Two Classes:
1) Measure of Central tendency or Location
, 2) Measure of Variability or Dispersion
We can also evaluate sampling error (accuracy), standard error, confidence limits
(intervals)
Inferential Statistics - Answers- Statistical tests used to test hypotheses.
Gives us a snapshot of what our data set is like.
Measures of Central Tendency or Location - Answers- Mean, Median, Mode
Measures of Variability or Dispersion - Answers- Variance, Range, Standard Deviation
Descriptive Statistics E.g. Adults in the United States BMI
Random sample of n=110, adult males in the U.S.
Random sample of adult males in the U.S. n=9 - Answers- We would look at the
frequency on the y=axis, and BMI on the x-axis.
X-axis: Measured variable
Y-axis: Frequency/Count
Histogram - Answers- A graph of vertical bars representing the frequency distribution of
a set of data.
AKA Frequency graph/distribution
Mean - Answers- the arithmetic average of a distribution, obtained by adding the scores
and then dividing by the number of scores
y (bar)= Sum of y/ n
y= data point
n=sample size
Population Mean: miu=sum of y/N (population size)
-Most commonly reported measure of central tendency.
Median - Answers- middle value of an ordered data set
-arrange data in ascending order.
-use this formula to determine which value is the median
y_(n+1) * 0.5
Mode - Answers- the most frequently occurring score(s) in a distribution
Types of Distributions - Answers- Normal, Negatively skewed, Positively skewed
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