Unit 1

A step-by-step process used by scientists to investigate questions, gather evidence, and draw conclusions based on experiments and observations

Scientific method

In the scientific method, we make an ______, ask a ______, propose a ______, design an ______, collect ______, and draw a ______

Observation, question, hypothesis, experiment, data, conclusion

Predictions that can be tested by recording more observations and experiments:

Hypothesis

What are hypotheses often heard as?

If …, then … (because..)

Does hypothesis have to be in this format: if…then…(because…)?

No

What is “if” in the hypothesis?

The manipulated variable

What is “then” in the hypothesis?

The responding variable

What is “because” in the hypothesis?

Optional explanation

Can results support or refute the hypothesis?

Either support or refute

Should you ever say “the hypothesis is correct”?

No

What hypothesis do we always start with?

Null hypothesis

What does null hypothesis provide?

Baseline that scientists can test against

What does testing against a baseline help to do?

Determine if results are significant or due to chance

A hypothesis in which the researcher attempts to disprove, reject, or nullify:

Null hypothesis

By attempting to reject the null, what can researchers support?

Their experimental hypothesis

By attempting to reject the null, what can researchers draw?

Meaningful conclusions

The hypothesis that there is no difference between two groups of data, and the experimental observations are due to chance:

Null hypothesis

The hypothesis that there is no significant difference between expected and observed data:

Null hypothesis

After the null, list the:

Alternative hypotheses

What to list when listing alternative hypotheses?

H1, H2, H3, etc.

Example of H1 and H2 alternative hypotheses:

H1: Medicine provide relief

H2: Medicine worsen symptoms

Types of experimental groups:

Control and experimental group

At least how many trials are needed for each experimental group?

3

What is the control group used for?

Comparison to experiemental group

What does control group help to validate?

Statistical analysis

What does control group increase?

Confidence in conclusions drawn from experimental results

What does experimental group receive?

Experimental treatment

In experiemental group, what is tested to observe impact on what?

IV on DV

Types of control group:

Negative and positive

Group not exposed to any treatment or to a treatment known to have no effect:

Negative control group

Group not exposed to the IV but is exposed to a treatment known to have an expected effect:

Positive control group

What does negative control group help to ensure when there should be no effect?

There is no effect

What does the positive control group ensure the experimental setup can produce?

Known effect

What does positive control group provide?

Reference point for what known effect looks like

Example of negative control group:

Pair treatment known to have no effect on heart rate with caffeine to test if it has effect

Example of positive control group:

Using established antibiotic known to work to compare with new antibiotic

What are statistics used to do to quantitative data?

Collect, process, interpret

How do statistics in biology help us understand important info?

By summarizing observations and making predictions based on summary

What do statistics in biology help scientists to avoid doing?

Jumping to conclusions and making generalizations

Methods used to summarize or describe observations/samples:

Descriptive statistics

Types of descriptive statistics:

Methods of central tendency and methods of variability

What do methods of central tendency involve?

Mean, mode, median

What do methods of variability involve?

Range, standard deviation

What do inferential statistics use observations to do?

Make estimates or predictions

What do inferential statistics generalize from sample to?

Wider population

Examples of inferential statistics:

Standard error of the mean, hypotheses tests

Examples of hypotheses tests:

Chi square, ANOVA, t-test

Are symmetrical distributions common?

Yes

In symmetrical distributions, where are most observations?

Near center of range of values

In symmetrical distributions, where are observations less likely located at?

Extremes

What are symmetrical distributions called?

Normal distribution

What shape is the curve representing normal distribution?

Bell shaped

Are symmetrical distributions universal?

No

What other distributions are there apart from symmetrical ones?

Skewed distributions

Graph of normal distribution:

The tendency of the observations to center around a particular value / category rather than spread evenly across the range / categories:

Central tendencies

Measures of central tendency:

Mean, median, mode

The average of the data set:

Mean

How to find mean?

Sum all data points and divide by number of data points

The middle number in a range of data points:

Median

How to find median?

Arrange data points in numerical order, middle number is median

How to find median if there is an even number of data points?

Average two middle numbers

What measurements is the median useful for?

Measurements with extreme values or abnormal distribution

Why is the median useful for measurements with extreme values or abnormal distribution?

It is not distorted by extreme large or small measurements

The value that appears most often in a data set:

Mode

What is the mode only useful for?

Describing distribution of data where mean and median not appropriate

Examples of data where mean and median are not appropriate:

Bimodal distribution, categorical data

The measure of how spread out or dispersed the values in a set of data are?

Variability

What is variability measured by?

Range and standard deviation

The difference between the largest and smalest values:

Range

Does large range have great or small variability?

Great

Does small range have great or small variability?

Small

How many values does range take into account?

2

How many values does standard deviation take into account?

All

A measure of how spread out the data is from the mean:

Standard deviation

Is data closer or farther from the mean for low standard deviation?

Closer

For low standard deviation, what is likely causing changes?

Independent variable

For high standard deviation, is data closer or farther from the mean?

Farther

For high standard deviation, what is likely causing changes?

Factors other than independent variable

The normal distribution is characterized by the relationship between what and what?

Mean and standard deviation

What can we state about the proportions of population for normal distribution?

What proportions lie between any two values of the variable

What is the standard deviation used as?

Unit of measurement

Average amount by which values deviate from mean:

Standard deviation

What does standard deviation divide a bell-shaped distribution into?

Parts of standard size

What does each part of bell-shaped distribution contain?

Known percentage of total observations

About ______% of observations lie within 1 standard deviation either side of mean for normal distribution

68

What are the observations lying within 1 standard deviation on either side of mean for normal distribution represented as?

± 1s

About ______% of observations lie within 2 standard deviations either side of mean for normal distribution

95

What are the observations lying within 2 standard deviations on either side of mean for normal distribution represented as?

± 2s

About ______% of observations lie within 3 standard deviations either side of mean for normal distribution

99

What are the observations lying within 3 standard deviations on either side of mean for normal distribution represented as?

± 3 s

What do each of the terms mean in the standard deviation formula?

∑=sum of, x=data point, x̄=mean, (n-1)=degrees of freedom, n=number of values

What is the standard error of the mean used to determine?

Precision of and confidence in mean value

What does standard error of the mean measure how well the mean of the sample represents?

True mean of population

What is standard error of the mean based on?

Standard deviation and number of data points

What does low standard error increase confidence in?

Sample mean is close to population mean

What is standard error often given as?

A range

In normal distribution, what does ± 1 SE encompass?

68% of sample means

In normal distribution, what does ± 2 SE encompass?

95% of sample means

In normal distribution, what does ± 3 SE encompass?

99% of sample means