Straightforward Statistics: Understanding The Tools Of Research

Straightforward Statistics Straightforward Statistics Understanding the Tools of Research Glenn Geher and Sara Hall 1 1 Oxford University Press is a department of the University of Oxford. It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide. Oxford New York Auckland  Cape Town  Dar es Salaam  Hong Kong  Karachi  Kuala Lumpur Madrid Melbourne Mexico City Nairobi  New Delhi  Shanghai  Taipei  Toronto  With offices in Argentina Austria Brazil  Chile Czech Republic France Greece  Guatemala Hungary Italy Japan Poland Portugal Singapore  South Korea Switzerland Thailand Turkey Ukraine Vietnam Oxford is a registered trademark of Oxford University Press in the UK and certain other countries. Published in the United States of America by Oxford University Press 198 Madison Avenue, New York, NY 10016 © Oxford University Press 2014 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, by license, or under terms agreed with the appropriate reproduction rights organization. Inquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above. You must not circulate this work in any other form and you must impose this same condition on any acquirer. Library of Congress Cataloging-in-Publication Data Geher, Glenn. Straightforward statistics : understanding the tools of research / Glenn Geher, Sara Hall.   pages cm Includes bibliographical references and index. ISBN 978–0–19–975176–1 1. Psychometrics.  2. Psychology—Mathematical models. 3. Psychology—Research.  4.  Statistics—Study and teaching (Higher)  I.  Hall, Sara, 1979–  II.  Title. BF39.G427 2014 150.1′5195—dc23 2013035850 1 3 5 7 9 8 6 4 2 Printed in the United States of America on acid-free paper Glenn: For my dad, who has encouraged mathematical reasoning across my life. And for my mom, who has convinced me, always, that all stars are within reach. Sara: To Benjamin, for everything, and to Jackson, Stella, Susanna, and Sailor, the best people I've ever met. Also to my parents, for giving me the confidence to live life fully and the ability to laugh about it. Contents Preface  xiii Acknowledgements  xvii 1. Prelude: Why Do I Need to Learn Statistics?  1 • • • • • • The Nature of Findings and Facts in the Behavioral Sciences  3 Statistical Significance and Effect Size  4 Descriptive and Inferential Statistics  6 A Conceptual Approach to Teaching and Learning Statistics  7 The Nature of this Book  8 How to Approach this Class and What You Should Get Out of It  8 • Key Terms  9 2. Describing a Single Variable  15 • • • • • • • • • • • • Variables, Values, and Scores  15 Types of Variables  16 Describing Scores for a Single Variable  18 Indices of Central Tendency  18 Indices of Variability (and the Sheer Beauty of Standard Deviation!)  21 Rounding  25 Describing Frequencies of Values for a Single Variable  26 Representing Frequency Data Graphically  28 Describing Data for a Categorical Variable  32 A Real Research Example  33 Summary  35 Key Terms  35 vi