Chapter 12: Quantitative Skills and Biostatistics

Summarizing and Presenting Data

There are six types of graphs you should be familiar with:

1. Bar graph
2. Pie graph
3. Histogram
4. Line graph
5. Box-and-whisker plot 6. Scatterplot

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A graph must include the following things:

A title, measured axes labeled with numbers, labels and units, and index marks a frame or perimeter data points that are clearly marked.

Types of Data

• Count data are generated by counting the number of items that fit into a category.
• Normal, or parametric, data is measurement data that fits a normal curve, or normal distribution, usually for a large sample
• The sample size (n) refers to the number of members of the population that are included in the study.
• The mean (x) is the average of the sample
• One limitation of mean is, it is influenced by outliers
• Nonparametric data often includes large outliers and do not fit a normal distribution.

Types of Experiments or Questions

• Hypothesis: A prediction of what the outcome of the experiment will be.
• Independent Variable: The factor that you, as the experimenter, will change between the different groups in the experiment
• Dependent Variable: The data that you measure during the experiment.
• Constants (Controlled Variables): The things that are the same
• Control Groups: Any group that is needed so you can.
• Statistical Significance: The trustworthiness of the results and the certainty you have in your conclusions.
• Time-course experiments look at how something changes over time. A line graph is usually used to present this type of data.
• Bar graphs are helpful to compare categories of data
• Box-and-whisker plots should be used for nonparametric data
• Association experiments look for associations between variables. They attempt to determine if two variables are correlated, and additional tests can demonstrate causation.
• Scatterplots are used to present data from association experiments.

Probability

P = a/n

The probability (P) that an event will occur is the number of favorable cases (a) divided by the total number of possible cases (n).

• The product rule is used for independent events and is also called the “AND rule.”
• The sum rule is used for studying two mutually exclusive events, and can be thought of as the “EITHER” rule.

Hypothesis Testing

• Hypothesis testing is used to determine if two groups are significantly different from each other.
• It starts with a null hypothesis, which is rejected or accepted, depending on how a calculated p-value or chi- square value compares to a standard value.
• Many experiments involve comparing two datasets or two groups, and a t- test can be used to calculate whether the means of two groups are different from each other.
• This test is most often applied to datasets that are normally distributed. A p-value equal to or below 0.05 is considered significant in most biology-related fields.
• A chi-square test is a statistical tool used to measure the difference between observed and expected data.

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