Necessary steps in factor analysis: Enhancing validation studies of educational instruments. The PHEEM applied to clerks as an example

Figures & data

Table

Practice points

Combine several psychometric criteria in factor analysis: scree plot, eigenvalues and minimum percentage of additionally explained variance (approximately 5%). Tighten the eigenvalues criterion to prevent overfactoring. Investigate the interpretability of more than merely the solution which seems best according to the psychometric criteria. Relate outcomes of factor analysis to existing theories. Report the analysis properly.

Table 1.  Psychometric and interpretability criteria applied in factor analysis

Criteria
Objective or psychometric criteria	1	Point of inflexion on the scree plot
	2	Eigenvalues > 1.5
	3	Proportion of variance accounted for is minimally approximately 5%
Interpretability criteria	4a	At least 3 variables with a loading >0.40 per factor
	4b	Variables of the same component measure the same construct
	4c	Variables loading on different components measure different constructs
	4d	The rotated factor pattern demonstrates simple structure

Figure 1. Scree plot of the eigenvalues of the factors.

Table 2.  Factor loadings and communalities of the final 3-factor solution^a

		Component
No.	Item	1	2	3	h^2
27	I have enough clinical learning opportunities for my needs	0.793	−0.020	−0.065	0.63
34	The training in this post makes me feel ready to be an SpR/consultant	0.752	−0.017	0.126	0.58
35	My clinical teachers have good mentoring skills	0.721	0.142	0.198	0.58
30	I have opportunities to acquire the appropriate practical procedures for my grade	0.685	−0.057	0.009	0.47
28	My clinical teachers have good teaching skills	0.678	0.170	0.156	0.51
36	I get a lot of enjoyment out of my present job	0.661	0.169	0.111	0.48
39	The clinical teachers provide me with good feedback on my strengths and weaknesses	0.660	0.092	0.158	0.47
29	I feel part of a team working here	0.658	0.108	0.055	0.45
6	I have good clinical supervision at all times	0.646	0.206	0.077	0.47
22	I get regular feedback from my seniors	0.636	0.190	0.213	0.49
15	My clinical teachers are enthusiastic	0.621	0.305	0.131	0.50
37	My clinical teachers encourage me to be an independent learner	0.607	0.012	0.159	0.40
33	Senior staff utilise learning opportunities effectively	0.601	0.150	0.253	0.45
2	My clinical teachers set clear expectations	0.581	0.123	0.299	0.44
5	I have the appropriate level of responsibility in this post	0.579	−0.037	0.305	0.43
23	My clinical teachers are well organised	0.542	0.264	0.318	0.46
32	My workload in this job is fine	0.467	0.237	0.140	0.29
19	I have suitable access to careers advice	0.419	0.266	−0.005	0.25
14	There are clear clinical protocols in this post	0.351	0.034	0.242	0.18
18	I have the opportunity to provide continuity of care	0.345	0.173	0.077	0.16
38	There are good counselling opportunities for junior doctors who fail to complete their training satisfactorily	0.313	0.052	0.307	0.20
7	There is racism in this post	0.075	0.661	−0.061	0.45
13	There is sex discrimination in this post	0.045	0.640	−0.041	0.41
11	I am bleeped inappropriately	0.081	0.591	−0.088	0.36
8	I have to perform inappropriate tasks	0.155	0.550	−0.054	0.33
25	There is a no-blame culture in this post	0.253	0.416	0.115	0.24
17	My hours conform to the New Deal	−0.019	0.410	0.183	0.20
20	This hospital has good quality accommodation for junior doctors, especially when on call	0.056	0.386	0.255	0.22
26	There are adequate catering facilities when I am on call	0.031	0.306	0.161	0.12
24	I feel physically safe within the hospital environment	0.092	0.201	0.115	0.06
16	I have good collaboration with other doctors in my grade	0.163	0.180	0.128	0.08
3	I have protected time at this post	0.095	−0.007	0.678	0.47
9	There is an informative junior doctors handbook	0.097	0.098	0.655	0.45
1	I have a contract of employment that provides information about hours of work	0.131	0.037	0.564	0.34
4	I had an informative introduction programme	0.347	0.050	0.546	0.42
12	I am able to participate actively in educational events	0.164	0.188	0.513	0.33
	Initial eigenvalues	9.4	2.1	1.8
	Explained variance after rotation	21.95%	7.63%	7.48%

Notes: h² communality estimates (estimates of the proportion of variance in a given variable explained by all components jointly).

^aThe scores on the italic items were reversed.