Quantitative Skills and Biostatistics

Descriptive statistics

Descriptive statistics

Used to summarize large datasets, present patterns in data, and communicate results.

Sample

A subset of the population being studied.

Population

A group of organisms of one species that interbreed and live in the same place at the same time.

Bar graph

Used if the data is parametric. It's a good idea to show variance of the data by including the standard error.

Pie graph

Usually used to summarize data that is collected as percentages, or the results of a genetic cross.

Histogram

Making one is like setting up bins, or intervals with the same range that cover the entire dataset.

Line graph

Useful for displaying data or information that changes continuously over time.

Box-and-whisker plot

Should be used for nonparametric data.

Scatterplot

Used to present data from association experiments. Each data point is plotted as a dot.

Quantitative data

Based on numbers or amounts that can be measured or counted.

Qualitative data

Data that is descriptive, subjective, or difficult to measure.

Count data

Generated by counting how many of an item fit into a category.

Measurements

Continuous, meaning that there is an infinitely number of potential measurements over a given range.

Normal or parametric data

Measurement data that fit a normal curve or distribution, usually when a large sample size is used.

Sample size

How many members of the population are included in the study.

Normal distribution

Any of a family of bell-shaped frequency curves whose relative position and shape are defined on the basis of the mean and standard deviation.

Mean

The average of the sample.

Standard deviation

Can determine if numbers are packed together or dispersed.

Standard error

Can be used to report how much a given dataset varies, and is calculated by dividing the standard deviation by the square root of the sample size.

Nonparametric data

Often include large outliers, and do not fit a normal distribution.

Histogram or frequency diagram

Give information on the spread of the data and the central tendencies.

Median

The middle number in a dataset. Determined by putting the numbers in consecutive number and finding the middle number. If there is an even amount of numbers, it is found by averaging the two middle numbers.

Mode

The most frequently recurring number in the dataset.

Range

The difference between the smallest and largest number in a sample.

Time-course experiments

Experiments that look at how something changes over time.

Dependent variable

The variable in a functional relation whose value is dependent upon, or influenced by, an independent variable.

Independent variant

The variable in a functional relation whose value is independent, or is not affected by other variables.

Comparative experiments

These experiments compare populations, groups, or events.

Association experiments

Look for association between variables.

Product rule

Used for independent events, and is also called the "and" rule. The probability of independent events occurring together is the product of their separate probabilities.

Sum rule

Used when studying two mutually exclusive events, and can be thought of as the "either-or-rule". The probability of either two events occurring is the sum of their individual probabilities.

t-test

Can be used to calculate whether the means of two groups are significantly different from each other. Often applied to datasets that are normally distributed.

p-value

A p-value equal to below 0.05 is considered significant in most biology-related fields.

Chi-square test

A statistical tool used to measure the difference between observed and expected data.

Null hypothesis

What you are expecting to happen.

Critical value

Expected values are compared to actual values, and a x^2 value is calculated. This value is compared to a critical value.

Degrees of freedom

Represents the number of independent variables in the data. Often, this is the number of possibilities being compared minus one.