R 中的 lmer 纵向分析对象内和时间点之间的差异

lmer longitudinal analyses in R for variance within subjects and between timepoints

我有以下纵向(3 Timepoints)数据集:

# A tibble: 504 x 6
      ID   Age Age_group Sex    Timepoint  outcome
   <int> <int> <fct>     <chr>  <chr>        <dbl>
 1 33714    15 Young     Male   bl        0.00103 
 2 35377    15 Young     Female bl        0.00106 
 3 38623    45 Older     Female bl        0.00103 
 4 38806    66 Older     Female bl        0.00114 
 5 39593    69 Older     Female bl        0.00113 
 6 39820    60 Older     Female bl        0.00113 
 7 39951    46 Older     Male   bl        0.000986
 8 40286    68 Older     Female bl        0.00107 
 9 40556     9 Young     Male   bl        0.00114 
10 40798    11 Young     Male   bl        0.00111 
# ... with 494 more rows

数据:

39820L, 39951L, 40286L, 40556L, 40798L, 40800L, 40815L, 43762L, 
50848L, 52183L, 52461L, 52577L, 53320L, 53873L, 54153L, 54206L, 
54581L, 55122L, 55267L, 55462L, 55612L, 55920L, 56022L, 56307L, 
56420L, 56679L, 57405L, 57445L, 57480L, 57725L, 57809L, 58004L, 
58215L, 58229L, 58503L, 59326L, 59327L, 59344L, 59361L, 59865L, 
60099L, 60100L, 60280L, 60384L, 60429L, 60493L, 60503L, 60575L, 
60603L, 60664L, 60846L, 61415L, 61656L, 61749L, 61883L, 62081L, 
62210L, 62285L, 62937L, 62983L, 63327L, 63329L, 64081L, 64328L, 
64418L, 64507L, 64596L, 65178L, 65250L, 65302L, 65478L, 65480L, 
65487L, 65572L, 65802L, 65935L, 65974L, 65975L, 65978L, 65991L, 
65995L, 66013L, 66154L, 66237L, 66245L, 66389L, 66396L, 66460L, 
66572L, 66589L, 67174L, 73230L, 73525L, 73539L, 73677L, 73942L, 
73953L, 74034L, 74113L, 74114L, 74427L, 74439L, 74607L, 74641L, 
74657L, 74794L, 74800L, 74836L, 74942L, 74952L, 74962L, 74969L, 
74977L, 74985L, 74989L, 75220L, 75229L, 75407L, 75653L, 75732L, 
75735L, 75757L, 75895L, 75898L, 76381L, 76559L, 76574L, 76594L, 
76595L, 76746L, 76751L, 76755L, 76759L, 76775L, 77088L, 77091L, 
77099L, 77134L, 77188L, 77203L, 77252L, 77304L, 77413L, 77453L, 
77528L, 77556L, 77585L, 77668L, 78262L, 79724L, 79730L, 79850L, 
79977L, 80052L, 80819L, 80901L, 80932L, 81064L, 81065L, 81071L, 
81098L, 81142L, 81175L, 33714L, 35377L, 38623L, 38806L, 39593L, 
39820L, 39951L, 40286L, 40556L, 40798L, 40800L, 40815L, 43762L, 
50848L, 52183L, 52461L, 52577L, 53320L, 53873L, 54153L, 54206L, 
54581L, 55122L, 55267L, 55462L, 55612L, 55920L, 56022L, 56307L, 
56420L, 56679L, 57405L, 57445L, 57480L, 57725L, 57809L, 58004L, 
58215L, 58229L, 58503L, 59326L, 59327L, 59344L, 59361L, 59865L, 
60099L, 60100L, 60280L, 60384L, 60429L, 60493L, 60503L, 60575L, 
60603L, 60664L, 60846L, 61415L, 61656L, 61749L, 61883L, 62081L, 
62210L, 62285L, 62937L, 62983L, 63327L, 63329L, 64081L, 64328L, 
64418L, 64507L, 64596L, 65178L, 65250L, 65302L, 65478L, 65480L, 
65487L, 65572L, 65802L, 65935L, 65974L, 65975L, 65978L, 65991L, 
65995L, 66013L, 66154L, 66237L, 66245L, 66389L, 66396L, 66460L, 
66572L, 66589L, 67174L, 73230L, 73525L, 73539L, 73677L, 73942L, 
73953L, 74034L, 74113L, 74114L, 74427L, 74439L, 74607L, 74641L, 
74657L, 74794L, 74800L, 74836L, 74942L, 74952L, 74962L, 74969L, 
74977L, 74985L, 74989L, 75220L, 75229L, 75407L, 75653L, 75732L, 
75735L, 75757L, 75895L, 75898L, 76381L, 76559L, 76574L, 76594L, 
76595L, 76746L, 76751L, 76755L, 76759L, 76775L, 77088L, 77091L, 
77099L, 77134L, 77188L, 77203L, 77252L, 77304L, 77413L, 77453L, 
77528L, 77556L, 77585L, 77668L, 78262L, 79724L, 79730L, 79850L, 
79977L, 80052L, 80819L, 80901L, 80932L, 81064L, 81065L, 81071L, 
81098L, 81142L, 81175L, 33714L, 35377L, 38623L, 38806L, 39593L, 
39820L, 39951L, 40286L, 40556L, 40798L, 40800L, 40815L, 43762L, 
50848L, 52183L, 52461L, 52577L, 53320L, 53873L, 54153L, 54206L, 
54581L, 55122L, 55267L, 55462L, 55612L, 55920L, 56022L, 56307L, 
56420L, 56679L, 57405L, 57445L, 57480L, 57725L, 57809L, 58004L, 
58215L, 58229L, 58503L, 59326L, 59327L, 59344L, 59361L, 59865L, 
60099L, 60100L, 60280L, 60384L, 60429L, 60493L, 60503L, 60575L, 
60603L, 60664L, 60846L, 61415L, 61656L, 61749L, 61883L, 62081L, 
62210L, 62285L, 62937L, 62983L, 63327L, 63329L, 64081L, 64328L, 
64418L, 64507L, 64596L, 65178L, 65250L, 65302L, 65478L, 65480L, 
65487L, 65572L, 65802L, 65935L, 65974L, 65975L, 65978L, 65991L, 
65995L, 66013L, 66154L, 66237L, 66245L, 66389L, 66396L, 66460L, 
66572L, 66589L, 67174L, 73230L, 73525L, 73539L, 73677L, 73942L, 
73953L, 74034L, 74113L, 74114L, 74427L, 74439L, 74607L, 74641L, 
74657L, 74794L, 74800L, 74836L, 74942L, 74952L, 74962L, 74969L, 
74977L, 74985L, 74989L, 75220L, 75229L, 75407L, 75653L, 75732L, 
75735L, 75757L, 75895L, 75898L, 76381L, 76559L, 76574L, 76594L, 
76595L, 76746L, 76751L, 76755L, 76759L, 76775L, 77088L, 77091L, 
77099L, 77134L, 77188L, 77203L, 77252L, 77304L, 77413L, 77453L, 
77528L, 77556L, 77585L, 77668L, 78262L, 79724L, 79730L, 79850L, 
79977L, 80052L, 80819L, 80901L, 80932L, 81064L, 81065L, 81071L, 
81098L, 81142L, 81175L), Age = c(15L, 15L, 45L, 66L, 69L, 60L, 
46L, 68L, 9L, 11L, 16L, 9L, 56L, 16L, 16L, 14L, 53L, 8L, 6L, 
63L, 14L, 10L, 15L, 13L, 15L, 8L, 9L, 9L, 8L, 9L, 9L, 13L, 58L, 
10L, 7L, 8L, 8L, 6L, 15L, 43L, 8L, 11L, 44L, 70L, 14L, 12L, 10L, 
16L, 12L, 10L, 6L, 13L, 67L, 11L, 12L, 13L, 10L, 66L, 13L, 14L, 
12L, 45L, 52L, 64L, 17L, 9L, 12L, 44L, 69L, 11L, 10L, 12L, 10L, 
10L, 70L, 54L, 45L, 43L, 54L, 14L, 42L, 44L, 16L, 15L, 43L, 45L, 
50L, 53L, 53L, 49L, 69L, 14L, 65L, 14L, 13L, 67L, 59L, 52L, 54L, 
44L, 62L, 69L, 10L, 63L, 57L, 12L, 62L, 9L, 53L, 54L, 66L, 49L, 
63L, 51L, 9L, 45L, 49L, 49L, 61L, 62L, 57L, 67L, 65L, 45L, 16L, 
55L, 64L, 67L, 56L, 52L, 63L, 10L, 62L, 14L, 66L, 68L, 15L, 13L, 
43L, 47L, 55L, 69L, 67L, 52L, 15L, 64L, 55L, 44L, 13L, 48L, 71L, 
64L, 13L, 50L, 61L, 70L, 57L, 51L, 46L, 57L, 69L, 46L, 8L, 11L, 
46L, 71L, 38L, 56L, 16L, 16L, 46L, 67L, 70L, 61L, 47L, 69L, 11L, 
13L, 18L, 10L, 57L, 18L, 18L, 15L, 54L, 10L, 8L, 64L, 15L, 12L, 
16L, 14L, 16L, 9L, 11L, 11L, 10L, 10L, 11L, 14L, 59L, 12L, 8L, 
9L, 9L, 8L, 16L, 44L, 9L, 13L, 45L, 71L, 16L, 13L, 12L, 18L, 
13L, 11L, 8L, 14L, 68L, 12L, 13L, 14L, 11L, 67L, 14L, 15L, 14L, 
46L, 53L, 65L, 18L, 11L, 14L, 46L, 70L, 12L, 12L, 13L, 11L, 11L, 
71L, 55L, 46L, 44L, 55L, 15L, 43L, 45L, 17L, 16L, 44L, 46L, 51L, 
55L, 54L, 50L, 70L, 15L, 66L, 15L, 14L, 68L, 60L, 53L, 55L, 46L, 
63L, 70L, 11L, 64L, 58L, 13L, 63L, 10L, 54L, 55L, 67L, 50L, 64L, 
52L, 11L, 46L, 50L, 50L, 62L, 63L, 58L, 68L, 66L, 46L, 18L, 56L, 
65L, 68L, 57L, 53L, 64L, 11L, 63L, 15L, 67L, 69L, 16L, 14L, 44L, 
48L, 56L, 70L, 68L, 53L, 17L, 65L, 56L, 45L, 14L, 49L, 73L, 65L, 
14L, 50L, 62L, 71L, 58L, 52L, 47L, 58L, 70L, 47L, 9L, 12L, 47L, 
72L, 39L, 57L, 18L, 18L, 47L, 68L, 71L, 62L, 48L, 70L, 12L, 14L, 
19L, 11L, 58L, 19L, 19L, 16L, 55L, 11L, 9L, 65L, 17L, 13L, 18L, 
16L, 18L, 11L, 12L, 12L, 11L, 11L, 12L, 16L, 60L, 13L, 9L, 11L, 
10L, 9L, 17L, 45L, 11L, 14L, 46L, 72L, 17L, 14L, 13L, 19L, 15L, 
12L, 9L, 15L, 69L, 14L, 14L, 15L, 12L, 68L, 16L, 17L, 15L, 47L, 
54L, 66L, 20L, 12L, 15L, 47L, 71L, 13L, 13L, 14L, 12L, 12L, 72L, 
56L, 47L, 45L, 56L, 16L, 44L, 46L, 19L, 18L, 44L, 47L, 52L, 56L, 
55L, 51L, 71L, 16L, 67L, 16L, 15L, 69L, 60L, 54L, 56L, 46L, 64L, 
71L, 12L, 65L, 59L, 14L, 64L, 11L, 55L, 57L, 68L, 51L, 65L, 53L, 
11L, 47L, 51L, 51L, 63L, 64L, 59L, 69L, 67L, 48L, 19L, 57L, 66L, 
69L, 59L, 54L, 65L, 12L, 64L, 16L, 68L, 70L, 17L, 15L, 45L, 48L, 
57L, 71L, 69L, 54L, 18L, 66L, 57L, 50L, 15L, 50L, 74L, 66L, 15L, 
51L, 63L, 72L, 59L, 53L, 48L, 59L, 71L, 48L, 10L, 13L, 48L, 73L, 
40L, 58L), Age_group = structure(c(1L, 1L, 2L, 2L, 2L, 2L, 2L, 
2L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 
2L, 1L, 1L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 
1L, 1L, 2L, 1L, 1L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 2L, 2L, 1L, 1L, 
1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 1L, 2L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 
2L, 2L, 1L, 2L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 1L, 2L, 
2L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 2L, 1L, 2L, 2L, 
2L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 
2L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 
1L, 2L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 2L, 2L, 
2L, 1L, 1L, 1L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 
1L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 1L, 1L, 
2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 1L, 2L, 1L, 2L, 2L, 2L, 
2L, 2L, 2L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 
2L, 2L, 2L, 2L, 1L, 2L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 
2L, 1L, 2L, 2L, 2L, 1L, 2L, 2L, 2L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 
2L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 
2L, 1L, 1L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 
1L, 1L, 2L, 1L, 1L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 2L, 2L, 1L, 1L, 
1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 1L, 2L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 
2L, 2L, 1L, 2L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 1L, 2L, 
2L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 2L, 1L, 2L, 2L, 
2L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 
2L), .Label = c("Young", "Older"), class = "factor"), Sex = c("Male", 
"Female", "Female", "Female", "Female", "Female", "Male", "Female", 
"Male", "Male", "Male", "Male", "Female", "Male", "Male", "Male", 
"Female", "Male", "Male", "Male", "Male", "Male", "Male", "Male", 
"Male", "Female", "Female", "Male", "Female", "Male", "Female", 
"Female", "Female", "Male", "Female", "Female", "Male", "Female", 
"Male", "Female", "Male", "Female", "Male", "Male", "Female", 
"Male", "Male", "Male", "Female", "Female", "Female", "Male", 
"Female", "Male", "Female", "Female", "Male", "Male", "Female", 
"Male", "Male", "Female", "Female", "Male", "Male", "Female", 
"Female", "Female", "Female", "Female", "Male", "Male", "Male", 
"Male", "Female", "Female", "Female", "Female", "Female", "Male", 
"Female", "Female", "Male", "Male", "Female", "Male", "Female", 
"Female", "Female", "Female", "Female", "Male", "Male", "Female", 
"Female", "Male", "Female", "Female", "Female", "Female", "Female", 
"Female", "Female", "Female", "Female", "Female", "Female", "Female", 
"Female", "Female", "Male", "Female", "Male", "Female", "Male", 
"Female", "Female", "Female", "Female", "Female", "Male", "Male", 
"Female", "Female", "Male", "Female", "Male", "Female", "Female", 
"Male", "Female", "Female", "Female", "Male", "Female", "Male", 
"Male", "Male", "Female", "Female", "Male", "Male", "Male", "Female", 
"Female", "Male", "Female", "Female", "Male", "Female", "Female", 
"Male", "Female", "Male", "Male", "Male", "Male", "Female", "Male", 
"Male", "Female", "Male", "Male", "Male", "Male", "Male", "Male", 
"Female", "Male", "Female", "Female", "Female", "Female", "Female", 
"Male", "Female", "Male", "Male", "Male", "Male", "Female", "Male", 
"Male", "Male", "Female", "Male", "Male", "Male", "Male", "Male", 
"Male", "Male", "Male", "Female", "Female", "Male", "Female", 
"Male", "Female", "Female", "Female", "Male", "Female", "Female", 
"Male", "Female", "Male", "Female", "Male", "Female", "Male", 
"Male", "Female", "Male", "Male", "Male", "Female", "Female", 
"Female", "Male", "Female", "Male", "Female", "Female", "Male", 
"Male", "Female", "Male", "Male", "Female", "Female", "Male", 
"Male", "Female", "Female", "Female", "Female", "Female", "Male", 
"Male", "Male", "Male", "Female", "Female", "Female", "Female", 
"Female", "Male", "Female", "Female", "Male", "Male", "Female", 
"Male", "Female", "Female", "Female", "Female", "Female", "Male", 
"Male", "Female", "Female", "Male", "Female", "Female", "Female", 
"Female", "Female", "Female", "Female", "Female", "Female", "Female", 
"Female", "Female", "Female", "Female", "Male", "Female", "Male", 
"Female", "Male", "Female", "Female", "Female", "Female", "Female", 
"Male", "Male", "Female", "Female", "Male", "Female", "Male", 
"Female", "Female", "Male", "Female", "Female", "Female", "Male", 
"Female", "Male", "Male", "Male", "Female", "Female", "Male", 
"Male", "Male", "Female", "Female", "Male", "Female", "Female", 
"Male", "Female", "Female", "Male", "Female", "Male", "Male", 
"Male", "Male", "Female", "Male", "Male", "Female", "Male", "Male", 
"Male", "Male", "Male", "Male", "Female", "Male", "Female", "Female", 
"Female", "Female", "Female", "Male", "Female", "Male", "Male", 
"Male", "Male", "Female", "Male", "Male", "Male", "Female", "Male", 
"Male", "Male", "Male", "Male", "Male", "Male", "Male", "Female", 
"Female", "Male", "Female", "Male", "Female", "Female", "Female", 
"Male", "Female", "Female", "Male", "Female", "Male", "Female", 
"Male", "Female", "Male", "Male", "Female", "Male", "Male", "Male", 
"Female", "Female", "Female", "Male", "Female", "Male", "Female", 
"Female", "Male", "Male", "Female", "Male", "Male", "Female", 
"Female", "Male", "Male", "Female", "Female", "Female", "Female", 
"Female", "Male", "Male", "Male", "Male", "Female", "Female", 
"Female", "Female", "Female", "Male", "Female", "Female", "Male", 
"Male", "Female", "Male", "Female", "Female", "Female", "Female", 
"Female", "Male", "Male", "Female", "Female", "Male", "Female", 
"Female", "Female", "Female", "Female", "Female", "Female", "Female", 
"Female", "Female", "Female", "Female", "Female", "Female", "Male", 
"Female", "Male", "Female", "Male", "Female", "Female", "Female", 
"Female", "Female", "Male", "Male", "Female", "Female", "Male", 
"Female", "Male", "Female", "Female", "Male", "Female", "Female", 
"Female", "Male", "Female", "Male", "Male", "Male", "Female", 
"Female", "Male", "Male", "Male", "Female", "Female", "Male", 
"Female", "Female", "Male", "Female", "Female", "Male", "Female", 
"Male", "Male", "Male", "Male", "Female", "Male", "Male", "Female", 
"Male", "Male", "Male", "Male", "Male", "Male", "Female"), Timepoint = c("bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", "bl", 
"bl", "bl", "flu1", "flu1", "flu1", "flu1", "flu1", "flu1", "flu1", 
"flu1", "flu1", "flu1", "flu1", "flu1", "flu1", "flu1", "flu1", 
"flu1", "flu1", "flu1", "flu1", "flu1", "flu1", "flu1", "flu1", 
"flu1", "flu1", "flu1", "flu1", "flu1", "flu1", "flu1", "flu1", 
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), class = c("tbl_df", "tbl", "data.frame"))

outcome 是在 timepoint-bl (1)、timepoint-flu1 (2) 和 timepoint-flu2 时对每个受试者 (ID) 进行采样的生理指标(3).每个对象 ageage_groupsex 也被记录下来。 Ageoutcome 的预测变量,sex 用作交互变量。

目标:

  1. 我正在尝试估计 outcome 变量 Young 和 [= 之间的斜率是否存在显着差异27=] 成人跨越 3 Timepoints.

  2. 我正在尝试估计 个人 (ID) outcometimepoints [=47] 之间的方差=]和 age_group.

这是为我的目标建模的正确方法吗?情节对我来说看起来不准确。我是线性混合模型的新手,因此不胜感激任何建议。

#mixed
DF_mixed <- lmer(outcome ~ Age* Sex + (1 + Age| Age_group:Timepoint) + (1|ID), data = DF) 
# identify age*sex interactions to predict outcome value between timepoints, nested in age_group that have random slope and intercepts

#plot
ggplot(DF, aes(x = Age, y = outcome, color = Timepoint)) +
      geom_point(alpha = 0.7) +
      theme_classic() +
      geom_line(data = cbind(DF, pred = predict(DF_mixed)), aes(y = pred), size = 1)   # adding predicted line from mixed model 



下面,我将介绍以下建议:(1) 准备数据,(2) 指定模型,以及 (3) 检查模型结果。

除了 tidyverse 包和 lme4,我将使用 broom.mixed::glance()tidy() 检查模型参数,并使用 ggeffects::ggpredict() 生成模型绘图预测。

library(tidyverse)
library(lme4)
library(broom.mixed)
library(ggeffects)

数据准备和变量选择

Timepoint 是一个字符,将被视为模型中的无序类别,这可能不是您想要的。通常最好使用自基线以来经过的实际时间而不是通用的“时间点”,尤其是在时间点之间的距离可变的情况下。对于这个答案,我根据每个受试者相对于基线的年龄变化计算了一个替代 Timepoint_yrs;但是如果你有更精确的时间记录,你可能想用它来代替。

此外,outcome 由一小部分值组成,大约为 1e-4 - 1e-3;这可能会导致 lmer 行为异常,因此我对其进行了缩放。

DF <- DF %>% 
  group_by(ID) %>% 
  mutate(Timepoint_yrs = Age - min(Age)) %>% 
  ungroup() %>% 
  mutate(outcome_scaled = as.numeric(scale(outcome)))

在模型中包含 AgeAge_group 会导致多重共线性问题,因为一个是另一个的函数。鉴于 Age 的极端双峰分布,我只使用了 Age_group。如上所述,年龄的变化现在由 Timepoint_yrs.

解释

型号规格

“我正在尝试估计 3 TimepointsYoungOlder 成年人的结果变量斜率是否存在显着差异” -- 即 Age_group 通过 Timepoint_yrs 交互。您还写道,"sex 用作交互变量。" 因此,将其放在一起,您正在查看 [= 的 3 向 Age_group 38=] 通过 Timepoint_yrs 互动。因为 Age_groupSex 仅在受试者之间有所不同,我们将在固定效应级别指定:

outcome_scaled ~ Age_group * Sex * Timepoint_yrs

因为每个人有多个测量值 (ID),我们将包括 ID:

的随机截距
outcome_scaled ~ Age_group * Sex * Timepoint_yrs + (1 | ID)

我们还可以允许 Timepoint_yrs 的斜率因人而异。从你的 post 来看,我没有看到是否包含随机斜率的强有力的理论依据——所以我们将两者都做,看看哪个模型最合适。

# model 1 - random intercepts
rnd_intercept <- lmer(outcome_scaled ~ Age_group * Sex * Timepoint_yrs + (1 | ID), data = DF) 

# model 2 - random intercepts and slopes
rnd_int_slope <- lmer(outcome_scaled ~ Age_group * Sex * Timepoint_yrs + (Timepoint_yrs | ID), data = DF)

模型结果

glance(rnd_intercept)
# # A tibble: 1 x 6
# sigma logLik   AIC   BIC REMLcrit df.residual
#   <dbl>  <dbl> <dbl> <dbl>    <dbl>       <int>
# 1 0.510  -575. 1170. 1212.    1150.         494

glance(rnd_int_slopes)
# A tibble: 1 x 6
#   sigma logLik   AIC   BIC REMLcrit df.residual
#   <dbl>  <dbl> <dbl> <dbl>    <dbl>       <int>
# 1 0.487  -575. 1173. 1224.    1149.         492

查看 AIC 和 BIC,随机截距模型似乎更好/更简约;由于没有任何理论上的理由更喜欢随机斜率模型,我们将坚持使用该模型。

tidy(rnd_intercept, conf.int = TRUE)
# # A tibble: 10 x 8
#    effect   group    term               estimate std.error statistic conf.low conf.high
#    <chr>    <chr>    <chr>                 <dbl>     <dbl>     <dbl>    <dbl>     <dbl>
#  1 fixed    NA       (Intercept)         -0.123     0.122    -1.01    -0.361     0.116 
#  2 fixed    NA       Age_groupYoung      -0.0142    0.221    -0.0643  -0.448     0.419 
#  3 fixed    NA       SexMale              0.248     0.214     1.16    -0.171     0.667 
#  4 fixed    NA       Timepoint_yrs        0.131     0.0407    3.21     0.0509    0.210 
#  5 fixed    NA       Age_groupYoung:Se~  -0.0704    0.317    -0.222   -0.692     0.551 
#  6 fixed    NA       Age_groupYoung:Ti~  -0.152     0.0654   -2.32    -0.280    -0.0234
#  7 fixed    NA       SexMale:Timepoint~  -0.0547    0.0771   -0.709   -0.206     0.0964
#  8 fixed    NA       Age_groupYoung:Se~   0.0192    0.101     0.190   -0.178     0.217 
#  9 ran_pars ID       sd__(Intercept)      0.862    NA        NA       NA        NA     
# 10 ran_pars Residual sd__Observation      0.510    NA        NA       NA        NA     

最后,我们可以绘制模型的预测值。您的原始代码为原始数据中的每一行预测了一个数据点,然后基本上在每行之间追踪了一条线,正如您所指出的,这不是很有用。相反,对于您的预测变量的每个独特组合,我们只想将绘图基于一个预测结果值(+/- 误差)。 ggeffects::ggpredict() 是一个很好的捷径; emmeans::emmeans() 是另一种选择。

plot_data <- ggpredict(rnd_intercept, terms = c("Timepoint_yrs", "Age_group", "Sex"))
# col names: x = Timepoint_yrs, group = Age_group, facet = Sex, predicted = observed_scaled

ggplot(plot_data, aes(x, predicted)) +
  geom_line(aes(color = group)) +
  geom_ribbon(aes(ymin = conf.low, ymax = conf.high, fill = group), alpha = .1) +
  facet_wrap(vars(facet)) +
  labs(x = "Years Since Baseline", y = "Outcome\n(scaled, model-predicted)") +
  theme_classic()

根据您的模型系数,您可能还想查看跨 Timepoint_yrsAge_group,以及跨其他变量折叠的 Timepoint_yrs 的主要影响。您可以通过将 terms 参数更改为 ggpredict() 并相应地修改 ggplot 规范来做到这一点。