Coding help - calculating IAT reliability

[Gemma Crickmore]

Hello,

Firstly, thank you so much for all of your useful posts about how to run an IAT in qualtrics with MinnoJS. With your help, I've successfully run my IAT and computed the D scores from the raw data using the blog post about processing the IAT data in R! Thank you so much! 

Unfortunately I'm not an R expert so I'm struggling with the final step for my study: finding a way to add to the script to calculate the reliability for my IAT, for example like the  IAT_rel() function from the ImplicitMeasures package.

Would you be able to help me with this?

Thanks so much in advance,

Gemma

[Yoav Bar-Anan]

Hi Gemma, 

Assuming you used the R script we posted here, after you get the data.frame iatscore in line 131, the iatscore should have the variables IAT1 and IAT2 for scores computed from the "practice" blocks (Blocks 3 and 6) and the "critical" blocks (Blocks 4 and 7).

From these two variables, there are multiple methods for computing reliability as internal consistency, using Spearman-Brown prophecy formula. I assume that is what iat_rel does (although this was not specified in the documentation I found).

Here are two examples:

############

# Method 1

#Compute correlation

correlation <- cor(iatscore$IAT1,  iatscore  $IAT2)

# Apply the Spearman-Brown prophecy formula
reliability <- 2 * correlation / (1 + correlation)

# Print the reliability
print(reliability)

############

# Method 2

library(psych)
# Calculate split-half reliability
split_half <- splitHalf(iatscore)
print(split_half)

Good luck,

Yoav

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