I have seen that the minimum alpha is .65 but normally the minimum alpha is considered to be .70 . This is in general research. I do not know in what field you are.

Deciding the minimum value of rho (ρ) often depends on the specific engineering context and the design codes or standards being followed. For example, in structural engineering, the minimum reinforcement ratio (ρ) is typically determined to ensure ductility and avoid brittle failure in concrete beams. Here are some general guidelines:

Structural Engineering:

• ACI 318 Code: The American Concrete Institute (ACI) Code 318 specifies minimum reinforcement ratios to ensure that the cracked concrete section is not stronger than the uncracked section. This helps prevent sudden failure and ensures ductility1.
• Formula: A common formula used is ρ_min = 0.0033 for normal-weight concrete. This value can vary based on factors like concrete strength and beam dimensions1.

Fluid Mechanics:

• Line Sizing: In fluid mechanics, the minimum rho (ρV^2) criteria might be used for line sizing to limit vibration in pipes. The specific value would depend on the fluid properties and the design requirements.

General Approach:

• Design Requirements: The minimum value of rho is often determined based on design requirements, safety factors, and material properties. It's important to refer to relevant codes and standards for specific values and calculations.

0.6 is the bare minimum acceptable value. Article Translation, Validity and Reliability of Decision Style Scal...

The mythology around the minimum value for alpha is so pervasive that no-one bothers to read the original paper by Nunally that is used to justify an alpha of 0·7 as being 'good' reliability. And notice that now people like s. Rama Gokula Krishnan are citing 0·6!! Standards are slipping day by day.

At this point it's worth quoting Nunally because it is simply baffling how anyone could have misread it so totally, and how no-one ever went back to check. Here's what he actually wrote :

"In the early stages of research… one saves time and energy by working with instruments that have only modest reliability, for which purpose reliabilities of ·70 or higher will suffice… In contrast to the standards in basic research, in many applied settings a reliability of ·80 is not nearly high enough… In many applied problems, a great deal hinges on the exact score made by a person on a test… In such instances it is frightening to think that any measurement error is permitted. Even with a reliability of ·90, the standard error of measurement is almost one-third as large as the standard deviation of the test scores."

So Nunally does not support low alphas and neither does any other actual statistical paper. He is calling an alpha of 0·7 'only modest reliability' and 0·8 is "not nearly high enough" in applied settings.

The urban legend that an alpha of 0.7 is acceptable for a measurement scale is just that: an urban legend. It is chronicled in a very amusing paper by Lance (Lance CE, Butts MM, Michels LC. The Sources of Four Commonly Reported Cutoff Criteria: What Did They Really Say? Organizational Research Methods. 2006 Apr 1;9(2):202–20. )

Ronán Michael Conroy I think you need to re-read the question again. The question is not about the ideal Chronbach Alpha value but the minimum acceptable level and that level happens to be 0.6. Apart from the source I already cited in my previous answer, let me point to Taber’s paper which has been cited more than 12,000 times. There, he analysed the acceptable values through an amalgamation of multiple studies published in leading scientific journals.

Read: https://link.springer.com/article/10.1007/S11165-016-9602-2

Those interested may examine this image which highlights this fact in the form of a simple figure.

Figure: https://link.springer.com/article/10.1007/s11165-016-9602-2/figures/1

As seen in this image, almost all the studies consider 0.6 as acceptable (poor but acceptable). Only 0.5 is considered unacceptable.

Riaz Ali You can cite Taber's paper that I have shared for your research. It is not his opinion alone that he has highlighted, but the levels which the scientific community has openly accepted. All the best.

s. Rama Gokula Krishnan – what mathematical basis have you for the assertion that 0·6 is acceptable. Acceptable according to what criteria? Science is not a religion, and an opinion is simply an opinion, however often it is repeated.