The way we (scientists) do things. SCIENTIFIC METHOD The way we (scientists) do things. Scientists have a unique way of looking at the world. They want to know more about their world. They follow a set of rules for governing their research.

OBSERVATIONS All of us make everyday observations. Observations lead to questions about the world around us. Scientists want answers to these questions.

Overview

Problem Statement A problem statement states the question raised by observations. Problem statements often begin with “why” or “how” or “what if.”

Research Maybe someone already knows the answer to your question. Sources include: - Past relevant experiments - Encyclopedias - Scientific Journals - RELIABLE Online Resources Must be in your OWN WORDS Proper Citing is important! Give credit where it is due

Hypothesis A hypothesis states what the scientist believes to be the answer to the problem statement. A hypothesis draws on all the background known about the problem. Hypotheses are formatted, “If,…then,…because….”

How to construct a GOOD hypothesis

Hypothesis Must be in IF-THEN-BECAUSE format! TESTABLE Independent Variable: The condition studied. It is controlled by the experimenter. ex. Water Dependent Variable: The condition affected by the ind. variable. It can’t be controlled by the experimenter. ex. Plant Growth Control: The condition that is represented in a normal situation

Constructing your “If” Statement 1. Start your sentence with the word “If” 2. Write down one of the variables 3. Connect statement with one of the following: is related to is affected by Causes 4. Write down the other variable

Constructing your “then” Statement - Write the word “then” (following the “if” section) - Make a comment on the relationship between those two variables. Ex. If section: If water is related to plant growth, Ex. Then section: then the more you water plants, the bigger they will grow.

Hypothesis Exercises Salt in soil may affect plant growth. Plant growth may be affected by the color of the light. Bacterial growth may be affected by temperature. Ultra violet light may cause skin cancer. Temperature may cause leaves to change color.

Test the Hypothesis Experiments test your hypothesis. The best experimental design is “controlled.”

Controlled Experimentation When designing the experiment, the researcher carefully controls as many variables as possible. Variables - things that may be expected to change during the course of an experiment. Ex.: temperature, humidity, sunlight, etc. Three types: Dependent variable – the one the investigator measures. Ex.: growth rate Independent – what the investigator deliberately changes during the experiment; factors that will directly affect the dependent variable. Ex.: amount or type of fertilizer, temperature, amount of water. ONLY ONE (1) independent variable can be tested at a time. Standardized (controlled) – factors that are kept equal for all groups. Ex.: If groups get different amounts of fertilizer, then the type of fertilizer must be the same for all groups.

How to Identify IV and DV Independent Dependent Cause Effect Before After Input Output What you do What happens

Examples Dependent Independent Cell phone bill Minutes used How far you drive Amount of gas you have Your 9 weeks grade Number of assignments turned in How much money you earn Hours you work Cost of a speeding ticket Miles over the speed limit Time it takes to drive somewhere How fast you drive Result of a football game Who scores more points Total calories and fat Number of hamburgers

Controlled Experimentation In most experiments there is a control group and experimental groups. The two groups are as similar as possible, but the treatment group is the one that experiences the variable that you’re studying. Control Group – group in which the independent variable is either eliminated or set at a standard value. You MUST have a control group in order to be able to measure the effects of your independent variable upon the dependent variable. Experimental Group(s) – groups which are being exposed to the independent variable.

Collect Data The results of an experiment are called “data.” Scientists use their five senses to collect data.

Collect Data Scientists often use specialized equipment to help them collect their data.

Analyze Data Now that you have your data, you must make sense of it. Scientists use: Charts Tables Graphs Equations

Making a Graph Often the goal of an experiment is to find the relationship between two variables (pressure and volume, time and temperature, etc.). As one variable changes, so does the other. Graphing is a useful way to visualize and describe these relationships.

Graphing Checklist Use the computer. If drawn by hand, graphs must be neat and on graph paper Usually, the x-axis is for the independent variable (manipulated) and the y-axis for the dependent variable (responding). Decide on the limits of the graph (maximum and minimum values). Make sure they are appropriate for the data series. Select divisions on the axes which are easy to read and use the space efficiently. Grid lines should be shown on the graph. Label both axes with both quantity and units. Ex: Volume (mL) Choose the correct graph for the type of data you are representing. Title the graph in a descriptive manner.

Pie Charts In a pie chart, each category is represented by a slice of the pie. The area of the slice is proportional to the percentage of responses in the category. Pie charts are effective for displaying the relative frequencies of a small number of categories. They are not recommended, however, when you have a large number of categories. Pie charts can also be confusing when they are used to compare the outcomes of two different surveys or experiments. For small samples, its better to use the actual # instead of percentages. Figure 1. Pie chart of iMac purchases illustrating frequencies of previous computer ownership.

Bar Graphs Bar charts can also be used to represent frequencies of different categories. A bar chart of the iMac purchases is shown in Figure 2. Frequencies are shown on the Y axis and the type of computer previously owned is shown on the X axis. Figure 2. Bar chart of iMac purchases as a function of previous computer ownership.

Line Graphs Usually measures frequency over a span of time. X-axis is always the length of time and Y-axis is the frequency.

What does the data mean? There are two options: The evidence supports the hypothesis. The evidence is inconsistent with the hypothesis.

What do you do? If the data is inconsistent with the hypothesis, you revise your hypothesis in light of your new information. Then you design a new experiment.

OK, I’ve got it all right. Now what? Tell everyone, silly! Scientists publish their findings to share what they’ve discovered with other scientists (and to brag a little, too.)

What do you do? If the data supports the hypothesis, you repeat the experiment several times to make sure you did everything right.

Summary