Science refers to a body of knowledge Science
§ Science refers to a body of knowledge § Science is not a giant collection of facts to be memorized. § It important to learn about the process of science called the scientific method. § The scientific method allows the solving of problems and answer questions. § Observations § Proposing ideas § Testing the ideas § Discarding or modifying ideas based on results © 2013 Pearson Education, Inc.
1. 1 The Process of Science The Nature of Hypotheses § Hypothesis: proposed explanation for a set of observations § Hypotheses needs to be: § Testable – it must be possible to examine the hypothesis through observations § Falsifiable – it must be able to potentially be proven false © 2013 Pearson Education, Inc.
Where do hypotheses come from? § Both logical and creative influences are used to develop a hypothesis © 2013 Pearson Education, Inc.
Scientific Theory § Powerful, broad explanation of a large set of observations § Based on well supported hypotheses § Supported by research from several different independent sources § As close to a “law” as you are going to get in Biology § Examples: Cell Theory, Evolutionary Theory © 2013 Pearson Education, Inc.
The Logic of Hypothesis Tests § Inductive reasoning: combining a series of specific observations into a generalization to create a hypothesis § Use specifics to generalize § For example: Dogs have hair. Dogs are mammals. Cats have hair. Cats are mammals. Therefore, all mammals must have lots of hair. § Is that necessarily true? § Can give a starting point to researching more © 2013 Pearson Education, Inc.
The Logic of Hypothesis Tests § To test the hypothesis use deductive reasoning: § This involves using a general principle to predict an expected observation using if/then statements § For example, If vitamin C decreases the risk of catching a cold, then people who take in additional Vitamin C will get less colds. © 2013 Pearson Education, Inc.
The Logic of Hypothesis Tests § The process looks something like this: © 2013 Pearson Education, Inc.
If people who take vitamin C suffer fewer colds than those who do not. . . If people who take vitamin C suffer the same number of colds or more than those who do not. . . Conclude that prediction is true Conclude that prediction is false Do not reject the hypothesis Reject the hypothesis Conduct additional tests Why should scientists consider alternative hypotheses even if their hypothesis is supported by their research? Consider alternative hypotheses © 2013 Pearson Education, Inc. Figure 1. 3 (continued)
The Logic of Hypothesis Tests § A hypothesis that fails our test is rejected and considered disproven. § A hypothesis that passes is supported, but not proven. § Why not? An alternative hypothesis might be the real explanation. © 2013 Pearson Education, Inc.
1. 2 Hypothesis Testing §The most powerful way to test hypotheses: do experiments!! © 2013 Pearson Education, Inc.
§Experiments support the hypothesis that the common cold is caused by a virus. (a) Cold–causing virus (b) How the virus causes a cold Nasal passages Host cell 1 Virus introduces its genetic material into a host cell. Virus Protein shell Throat Genetic material and proteins Virus copies 2 The viral genetic material instructs the host cell to make new copies of the virus. Immune system cells target infected host cells. Side effects are increased mucus production and throat irritation. 3 New copies of the virus are released, killing host cell. These copies can infect other cells in the same person or cells in another person (for example, if transmitted by a sneeze). Released virus copies Immune system cells Mucus © 2013 Pearson Education, Inc. Figure 1. 4
Find 2 steps in this process where drugs or therapies might disrupt the infection, prevent spreading or lessen symptoms. (a) Cold–causing virus (b) How the virus causes a cold Nasal passages Host cell 1 Virus introduces its genetic material into a host cell. Virus Protein shell Throat Genetic material and proteins Virus copies 2 The viral genetic material instructs the host cell to make new copies of the virus. Immune system cells target infected host cells. Side effects are increased mucus production and throat irritation. 3 New copies of the virus are released, killing host cell. These copies can infect other cells in the same person or cells in another person (for example, if transmitted by a sneeze). Released virus copies Immune system cells Mucus © 2013 Pearson Education, Inc. Figure 1. 4
The Experimental Method § Experiments are designed to collect data or information to test specific hypotheses. § Variables: factors that can change in value under different conditions § Independent variables can be manipulated by the scientist § In ideal experimental conditions, you only want to manipulate 1 variable at a time – why? § Dependent variables cannot be changed by the researcher © 2013 Pearson Education, Inc.
Controlled Experiments § Controlled experiment: tests the effect of a single variable § Control: a subject who is not exposed to the experimental treatment but has all other variables the same © 2013 Pearson Education, Inc.
Controlled Experiments § Differences seen between the experimental group and control group can be attributed to the experimental treatment. § Random Assignment § An effective way of assigning individuals to groups for testing © 2013 Pearson Education, Inc.
Animation: Science as a Process: Arriving at Scientific Insights Click “Go to Animation” / Click “Play” © 2013 Pearson Education, Inc.
Controlled Experiments § Example: Echinacea tea experiment: § Hypothesis: drinking Echinacea tea relieves cold symptoms § Experimental group drinks Echinacea tea 5 -6 times daily. § Control group drinks “sham” Echinacea tea 5 -6 times daily (placebo). § Both groups rated the effectiveness of their treatment on relieving cold symptoms. © 2013 Pearson Education, Inc.
Controlled Experiments § People who received echinacea tea felt that it was 33% more effective at reducing symptoms. © 2013 Pearson Education, Inc.
Minimizing Bias in Experimental Design § If human subjects know whether they have received the real treatment or a placebo, they may be biased. § Blind experiment: subjects don’t know what kind of treatment they have received § Double blind experiment: the person administering the treatments and the subjects do not know who is in each gropu until after the experiment is over © 2013 Pearson Education, Inc.
Minimizing Bias in Experimental Design © 2013 Pearson Education, Inc.
Using Correlation to Test Hypotheses § The “gold standard” for experimentation § Double-blind, placebo controlled and randomized experiments § Model systems can be used in experiments when it appears to dangerous or unethical to test on humans § examples: mice, rats, dogs and pigs § A correlation can be used to test hypotheses when controlled experiments on humans is impossible to perform © 2013 Pearson Education, Inc.
Using Correlation to Test Hypotheses § Using existing data, is there a correlation between variables? § Hypothesis: stress makes people more susceptible to catching a cold § Is there a correlation between stress and the number of colds people have caught? © 2013 Pearson Education, Inc.
Using Correlation to Test Hypotheses § Results of such a study: the number of colds increases as stress levels increase. § Caution! Correlation does not imply causation. © 2013 Pearson Education, Inc.
Using Correlation to Test Hypotheses § The correlation might be due to other reasons. © 2013 Pearson Education, Inc.
Overview: What Statistical Tests Can Tell Us § Statistics in science is used to evaluate and compare data. § We can extend the results from small samples to an entire population using statistical tests. § Statistically significant: results of difference between groups is due to random chance and not an error in experimenting © 2013 Pearson Education, Inc.
The Problem of Sampling Error §Sampling error: the effect of chance § We can calculate the probability that a result is simply due to sampling error. §Statistically significant: an observed difference is probably not due to sampling error §Opinion polling before a recent election indicated candidate A was favored by 47% of likely voters, and candidate B was favored by 51% of voters. There was a error of 3%. Why was this poll a statistical tie? © 2013 Pearson Education, Inc.
The Problem of Sampling Error §Confidence interval: the range of values from a sample that has a 95% probability of containing the true population mean (average). §Much population variation = large confidence interval §Small population variation = small confidence interval © 2013 Pearson Education, Inc.
The Problem of Sampling Error © 2013 Pearson Education, Inc. §The one circled on the left is better – see how the red lines don’t meet? You can say with confidence that there is a difference
Factors that Influence Statistical Significance § Sample size § The true difference between populations § Bigger is better: more likely to detect differences © 2013 Pearson Education, Inc.
Factors that Influence Statistical Significance © 2013 Pearson Education, Inc.
§A study followed 80, 000 women over 20 years §Some ate lots of white flour and sugar, low vegetable fat and protein §Others ate low amounts of refined carbs, and more vegetables and protein and had 30% less cases of heart disease §Where does this fall on chart? §What is the hypothesis? Difference between groups? Sample size? © 2013 Pearson Education, Inc. Figure 1. 15
§A study followed 80, 000 women over 20 years §Some ate lots of white flour and sugar, low vegetable fat and protein §Others ate low amounts of refined carbs, and more vegetables and protein and had 30% less cases of heart disease §Where does this fall on chart? 30% 80, 000 women © 2013 Pearson Education, Inc. Figure 1. 15
What Statistical Tests Cannot Tell Us § If an experiment was designed and carried out properly § If observer error occurred, only can evaluate the probability of sampling error § May not be of any biological significance © 2013 Pearson Education, Inc.
1. 4 Evaluating Scientific Information Primary Sources § Researchers can submit a paper about their results to a professional journal (primary source). § Primary Sources undergo peer review: evaluation of submitted papers by other experts § Journal of Molecular Biology § Journal of Biomedical Sciences § Journal of Immunology § Secondary sources: books, news reports, the internet, and advertisements © 2013 Pearson Education, Inc.
Information from Anecdotes § Anecdotal evidence is based on one person’s experience, not on experimental data. § Example: a testimonial from a celebrity © 2013 Pearson Education, Inc.
Science in the News © 2013 Pearson Education, Inc.
Science in the News § Secondary sources may be missing critical information or report the information incorrectly. § Consider the source of media reports. § Be careful with the internet since anyone can post information. § Be very cautious about claims made in paid advertisements. © 2013 Pearson Education, Inc.
Understanding Science from Secondary Sources § Use your understanding of the process of science to evaluate science stories. § News media generally highlight only those science stories that seem newsworthy. © 2013 Pearson Education, Inc.
1. 5 Is There a Cure for the Common Cold? § No, but prevention methods are known. § Wash your hands! § No effect on cold susceptibility: § Vitamin C § Exposure to cold temperatures § Exercise § No vaccine for the common cold © 2013 Pearson Education, Inc.
§Now let’s review with some questions: © 2013 Pearson Education, Inc.
A(n) ____ is a proposed explanation for a single observation. §scientific method §hypothesis §scientific theory §experiment © 2013 Pearson Education, Inc.
Which of the following is a scientific hypothesis? §Jazz is better music than rap. §Garden fairies make tomatoes grow better. §Hunting species to extinction is wrong. §Increasing the amount of protein in a cow’s diet increases her milk yield. © 2013 Pearson Education, Inc.
Which of the following is correct? §A hypothesis can be wrong. §A hypothesis is not always testable. §A hypothesis can prove a person’s values. §A hypothesis should be formed before making any observations. © 2013 Pearson Education, Inc.
In an experiment, Dr. Smith feeds different amounts of protein to dairy cows and measures the differences in their milk yields. What is the independent variable? §time §milk yield §amount of protein §placebo © 2013 Pearson Education, Inc.
What is happening in step #2 in the diagram? §The virus is introducing its genetic material into the cell. §The host cell is killed. §Copies of the virus are being made by the host cell. §The virus is being destroyed by the host cell. © 2013 Pearson Education, Inc.
What does this graph show? §There is no difference between placebo and zinc lozenges. §Taking placebo lozenges causes people to have more types of cold symptoms. §Zinc lozenges lead to people catching fewer colds. §People taking zinc lozenges show cold symptoms for a shorter period of time. © 2013 Pearson Education, Inc.
The confidence interval is the range of values that has a _____ probability of containing the true population mean. § 5% § 30% § 75% § 95% © 2013 Pearson Education, Inc.
A statistical test evaluates the chance of _____. §observer error. §sampling error. §alternative mechanisms. §need for controls. © 2013 Pearson Education, Inc.
Which of these statements about primary and secondary sources are correct? §Primary sources are written by researchers; secondary sources are written by book authors, news reporters, and advertisers. §Primary sources aren’t biased; secondary sources are biased. §Primary sources are not peer reviewed; secondary sources are peer reviewed. §Primary sources are less reliable; secondary sources are more reliable. © 2013 Pearson Education, Inc.
What is the best way to prevent the common cold? §Take vitamin C. §Wash your hands. §Take zinc lozenges. §Get a cold vaccine. © 2013 Pearson Education, Inc.
- Slides: 50