What are /r/psychometrics' favorite Products & Services?

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de Ayala's The Theory and Practice of Item Response Theory is a classic text:

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>Designed for researchers, psychometric professionals, and advanced students, this book clearly presents both the "how-to" and the "why" of item response theory (IRT). It describes simple and more complex IRT models and shows how they are applied with the help of widely available software packages. Chapters follow a consistent format and build sequentially, taking the reader from model development through the fit analysis and interpretation phases that one would perform in practice. The use of common empirical data sets across the chapters facilitates understanding of the various models and how they relate to one another.

You could also check out assess.com! They have a lot of good resources on the steps of making a psychometrically sound assessment. Or if it will be more of a credentialing exam this is also a resource I use a lot: https://www.amazon.com/Testing-Professions-Credentialing-Applications-Educational-ebook/dp/B06XPPT42B/ref=nodl_

Either Handbook of Modern Item Response Theory

or Multidimensional Item Response Theory

MIRT book handles much more than just multidimensional theory and uses slope-intercept form to discuss IRT and many folks much prefer that form.

Relevant: Naglieri & Jensen (2002), Reynolds & Jensen (1983).

I say this in the nicest way possible: it looks to me like you're in over your head. I'd recommend getting your hands on a classical test theory textbook like Crocker and Algina.

For the Mean, you're not looking for the mean frequency. You're looking for the mean total score for people who selected that option.

Step 1: score each response against the key

Step 2: calculate total score for each candidate

Step 3: find the sum of total scores for candidates who selected the option

Step 4: divide that sum by the number of candidates who selected the option

Hope that helps.

Edit to add: you can't calculate a standard deviation for a single score.

A Quick Review of Statistical Thinking https://www.amazon.com/dp/B07W452HCN/ref=cm_sw_r_cp_api_glc_KR05Fb4G1FY71

My undergrad advisor wrote and self-published this. He has a very no-nonsense approach to writing and I’ve used this as a reference many many times. My favorite saying (of many) from him was: “SPSS is easy if you ignore what you don’t need”