This contribution to the methodology series focuses on two issues relevant to all research projects: reliability and validity. There are many types of reliability and validity, and to make this contribution more grounded in previous columns, the reliability and validity of survey instruments will be the focus of this paper. A future paper will incorporate other aspects of validity (e.g., internal and external validity) when discussing the strengths and weaknesses of different methodological designs. The authors welcome comments from all readers who have suggestions about the way information is presented or questions about the content of this column. It is not comprehensive and does not replace information found in textbooks or peer-reviewed articles. Beyond their experience, the authors have used textbooks and articles as sources and recommend that you also refer to them for more detailed explanations of what is discussed in this column.Scenario: When we last met Allan and Gwen, they discussed different issues that needed to be considered before conducting a survey. Since that discussion, Gwen has identified some survey questions that might fit Allan's needs. She calls to inform him about what she has discovered. Their conversation follows.Gwen: Hi again, Allan. I've made progress on identifying some survey questions that might be helpful for your study. As we discuss the questions, I'd like to take this opportunity to also discuss the importance of reliable and valid measurement. I think we should start by discussing some terminology. How does that sound? If that sounds OK, we can start by discussing a construct. We discussed this previously, but it is so important that I think we need to revisit it to make sure we are on the same page.Allan: That sounds good, Gwen.Gwen: OK. Construct is the term for something we want to measure and can do so only indirectly through indicator variables (for example, a survey question). Because of such indirect measurement, constructs represent latent variables. An example of direct measurement is weight in pounds: you can stand on a scale and we can get a measure of how much you weigh. In this case, we can directly measure weight. An indirect measurement in the same situation would mean that I would ask you how much you weigh. In this case, this indirect measure helps us understand a construct called weight. We can't always collect direct measurements, so sometimes we rely on indirect measurements.In the study you want to do, peoples' perceptions about nature are indirect measurements. We are unable to measure exactly what they are thinking/feeling with respect to trees, green spaces, water, etc., so we rely on the next best approach: asking them about their perceptions. In your study, then, we have a number of constructs-trees, green spaces, water features, etc.- that we want to measure.Allan: Makes sense so far. Can we just ask study participants one question about each of these constructs?Gwen: Actually, we will want to ask more than one question about each construct. Usually, we try to measure constructs with at least three good survey items. Given that we do not know which items will be good when we start our research project, we actually try to use more than three survey items per construct. Items that are good are retained and items that are not good are discarded and not used again in the future. A reasonable rule of thumb is to write four or five items and then narrow these down to three items based on pilot testing-asking a small sample of people to take and evaluate your survey for comprehension and content relevance.One reason for using at least three survey items is to be able to estimate whether our measurement of each construct is internally consistent. Internal consistency provides information about the reliability of a survey (Etchegaray & Fischer, 2006). A specific measure of internal consistency is Cronbach's alpha, which measures the average intercorrelation of all survey items for a construct. …