Scientific Method Create testable operational definitions Be curious. Question your world. Collect data using DESCRIPTIVE Research Conduct more research Naturalistic Observation Survey Case Study Form a Hypothesis Relationship? CORRELATION Causation? EXPERIMENT Doesn’t support the hypothesis Continue to retest Use this to predict and explain the world Supports the hypothesis Create a Theory Essential Question • 1-5 How do psychologists draw appropriate conclusions about behavior from research? “The root of the problem is that in real life, all scientists ever observe are samples. And, in real life, all they want to know about is populations” Nancy Darling, Ph.D. The Importance of Sampling in Research • Sample – Small representative subset of a larger population • Random sample – Every subject had equal chance of being selected • Representative sample – Characteristics of participants correspond to larger population • Example: If we know approximately 15% of the United States’ population is of Hispanic descent, a sample of 100 Americans also ought to include around 15 Hispanic people to be representative. You want to make a claim about a WHS student. • What is the Population? – All WHS Students • What will be the sample? – The participants in the sample • How could you obtain a random sample? – Get the student list from the office and pick every 10th student. – Pull names out of a hat? • Why might you want a representative sample – A random sample won’t account for small populations • • • • Ethnic Groups AP Students Transitional Students Students in Life Skills Survey Random Sampling From a population if each member has an equal chance of inclusion into a sample, we call that a random sample (unbiased). If the survey sample is biased, its results are wrong. The fastest way to know about the marble color ratio is to blindly transfer a few into a smaller jar and count them. Sampling in Surveys • Women and Love study done by Shere Hite 1974 • 98% Dissatisfied by their Marriage • 75% Extramarital Affairs • But to all of those who were mailed surveys only 4% responded. When randomly sampled • 93% of women are satisfied in their marriages • Only 7% had affairs Making Inferences When is an Observed Difference Reliable? 1. Representative samples are better than biased samples. 2. Less variable observations are more reliable than more variable ones. 3. More cases are better than fewer cases. Making Inferences When is a Difference Significant? When sample averages are reliable and the difference between them is relatively large, we say the difference has statistical significance. For psychologists this difference is measured through p value below .05 Random Assignment • 100 Volunteers for an experiment • How do you choose which ones will be in the control group? Essential Question • 1-5 How do psychologists draw appropriate conclusions about behavior from research?

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# The Importance of Sampling in Research