Table 2 Spearman and Cronbach’s alpha correlation of the items of PDQ-39 and PDQ-8 for item-to-scale internal consistency in Iranian Parkinson’s disease patients (n = 114)

Mobility

Q1

0.648

0.674

0.916

Q2

0.722

0.743

0.913

Q3

0.818

0.777

0.910

Q4

0.842

0.773

0.910

Q5

0.719

0.677

0.915

Q6

0.719

0.649

0.917

Q7*

0.768

0.757

0.911

Q8

0.742

0.767

0.910

Q9

0.606

0.566

0.921

Q10

0.704

0.672

0.916

PDQ-8-1

0.832

-

Total = 0.922 (95% CI: 0.899-0.942)

Activity of daily living (ADL)

Q11

0.748

0.773

0.858

Q12*

0.814

0.804

0.852

Q13

0.857

0.767

0.858

Q14

0.675

0.474

0.906

Q15

0.738

0.707

0.867

Q16

0.697

0.740

0.863

PDQ-8-2

0.763

-

Total = 0.888 (95% CI: 0.852-0.917)

Emotional well being

Q17*

0.764

0.665

0.820

Q18

0.618

0.587

0.834

Q19

0.738

0.736

0.807

Q20

0.604

0.512

0.848

Q21

0.800

0.695

0.813

Q22

0.764

0.623

0.828

PDQ-8-3

0.758

-

Total = 0.850 (95% CI: 0.803-0.889)

Stigma

Q23

0.815

0.717

0.821

Q24

0.705

0.530

0.891

Q25*

0.857

0.801

0.787

Q26

0.874

0.803

0.783

PDQ-8-8

0.831

-

Total = 0.862 (95% CI: 0.815-0.899)

Social support

Q27*

0.853

0.408

0.745

Q28

0.660

0.543

0.505

Q29

0.566

0.598

0.521

PDQ-8-4

0.680

-

Total = 0.675 (95% CI: 0.556-0.766)

Cognition

Q30

0.645

0.334

0.696

Q31*

0.689

0.575

0.540

Q32

0.699

0.568

0.542

Q33

0.680

0.393

0.656

PDQ-8-5

0.668

-

Total = 0.677 (95% CI: 0.568-0.764)

Communication

Q34

0.833

0.424

0.691

Q35*

0.727

0.579

0.413

Q36

0.584

0.518

0.590

PDQ-8-6

0.649

-

Total = 0.662 (95% CI: 0.539-0.757)

Bodily discomfort

Q37*

0.809

0.520

0.458

Q38

0.813

0.477

0.524

Q39

0.583

0.383

0.640

PDQ-7

0.806

-

Total = 0.646 (95% CI: 0.516-0.745)